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Old 06-09-2017, 10:42 AM   #1
trottida
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Default Looking for a GM Tech/Specialist

I'm putting this out there with hopes that one of you may be able to give me some help on an HVAC issue I'm struggling with on my 2005 Suburban Z71. I haven't found anybody that describes having the same issues I'm experiencing and I've posted in a couple GM forums but I'm not getting any input back.

Any of you a GM Tech or know one? Take a look at this post on the GM-Trucks forum ....

2005 Chevrolet Suburban Z71 HVAC Issues

...
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Old 06-09-2017, 12:16 PM   #2
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Default Re: Looking for a GM Tech/Specialist

Would this help (new $153) ??

http://www.ebay.com/itm/AC-Delco-HVA...3D111821430958

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Old 06-09-2017, 12:24 PM   #3
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Default Re: Looking for a GM Tech/Specialist

I have a 2003 Suburban which has just been into the workshop for AC work.

For over a year I've had an issue with the ac working fine then slowly gets to the point where at traffic lights, etc it would blow warm, then once on the go it would blow cold again.

I took it into my indi garage who last year found that both hi & lo schrader valves were leaking, so they were replaced and it ran ok for a while, but the warm/cold symptoms kept coming back. My guy said you have a leak somewhere, but is only small?

I also found that the rear ac unit would blow cold and the front would blow warm, even though they share the same refrigerant! I too researched on Sub forums and Google, etc. The only thing I could find was that the front evaporator core, buried deep in the dash, can and does leak over time.

About 1 month ago, the ac was doing its party piece of warm at lights and cold on the run, so of it went back to the garage. The guy said that it was a sign of low refrigerant. Dye was injected into the system and the whole system full recharged and we kept a careful eye on this. I must have taken it back 3 or 4 times and watched the mechanic go over with the UV light from front to back. We even removed the side cover at the back of the truck to reveal the rear ac system and still no sign of dye.

We came to the conclusion that the issue was likely front evaporator core, which is located inside the hvac unit deep within the dash. To get to it involves basically dismantling the whole of the dash!!

So I bit the bullet on what I termed the nuclear option and gave them the go ahead to tear into it. It did actually turn out to be the evaporator core, which was gunged up to hell and leaking. After 14 years of service in Florida, not surprising. The green dye was in the bottom of that part of the system.

In addition, I was also suffering from an irritating squeaking on the drivers side, which we diagnosed as the Mode Actuator gone bad. There are about 4 or 5 various Actuators on the system all controlling various actions. I sourced that particular Mode Actuator myself and was going to swap it out myself. However with the Hvac unit in the truck, it's way under the dash and a complete pits to get access to. So as the hvac was being removed from the Sub, the guys installed it (2 hex screws and easy peasy with the hvac unit out).

I have the truck back and so far in this first week it seems to be working now as it should be.

The labor charge came out at a tad under $640.00 with evaporator and drier adding another $160.00. The dismantling job runs to about 8 hours labor.

If you end up having to replace the evaporator, this video shows what's involved. It's grim watching what they have to dismantle.

https://www.youtube.com/watch?v=yoDzJK1Bq2A

As for the ambient sensors on the Suburban, as you may know they are located in the roof headlining panel and look like microphone housings (a common mistake). You have 2 and they are both the same unit. They are basically a very small fan unit. I guess the fan sucks in the air and the sensor determines temperature, etc. Over time these fans become noisy and need replacing. I replaced the front one on mine 2 years ago. I bought online for $23.00 and it's basically plug & play. You just have to remove the B pillar trim and pull down the headlining to the point where you can get your hand in to remove the sensor. The rear one should be the same arrangement.

Hope this helps.

Last edited by floridasl22002; 06-09-2017 at 12:35 PM..

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Old 06-09-2017, 12:43 PM   #4
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Default Re: Looking for a GM Tech/Specialist

Quote:
Originally Posted by toggenburg View Post
I already bought one through Amazon.ca, installed it yesterday and determined that is was not the issue.

Cost me $240 CAD after taxes and I'm suspicious that it came from RockAuto as the RA cost with shipping came up to exactly the same amount to the penny. Amazon is pretty good with returns.

...
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Old 06-09-2017, 12:53 PM   #5
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Default Re: Looking for a GM Tech/Specialist

Quote:
Originally Posted by floridasl22002 View Post
I have a 2003 Suburban which has just been into the workshop for AC work.........

........Hope this helps.
It helps somewhat but doesn't explain the heat issues and the condenser fan not turning on.

This all started a couple years ago and at that time they replace the AC lines that run from the front to the rear (about 12 feet of preformed Aluminum line!). Last year they replaced the rear evaporator as it developed a leak. This spring the system was discharged again and they couldn't find a leak. They held a vacuum on it for a couple hours. It's charged and cools as long as your moving or keep the RPM's up.

I swapped the front and rear inside air temp sensors last night to see if the front one was bad. No change. I've ordered the temp sensor that is in the dash duct-work and it'll be here Monday. It was only $10 so I'm okay throwing a part at the problem.

I imported this Burb from Texas in 2013 so I imagine the AC is well used. The mileage was at 132K mi when I got it.

...
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Last edited by trottida; 06-09-2017 at 01:03 PM..

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Old 06-09-2017, 01:17 PM   #6
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Default Re: Looking for a GM Tech/Specialist

You have the main control unit on the dash, which when adjusted by you instructs the various actuators to do their job. If the control unit is working correctly, then it could be an Actuator solenoid or more that are not working correctly.

The Suburban HVAC system is a complicated piece of kit. I'm guessing yours is like mine, where besides the auto control unit in the dash, you have the additional controls for the rear ac above the rear view mirror and also more hvac controls for the rear passengers located at the rear of the console. So there are 3 sets of controls which can all muck up the system from operating correctly.

One thing I noticed with mine was that the rear ac was dripping the water condensation fine but the front wasn't doing as well, if at all. I made sure the drains were not plugged by clearing them out. The rear drain stares you in the face and is easy to rod. To gain access to the front drain, you need to jack up the truck on the passenger side, remove the wheel, then remove the plastic fender liner. That's the only way to get access to the front drain. I used a 14" long piece of old vacuum tube to rod mine. The tube came out clean and dry each time, which told me the drain was clear but there was something not right going on in the front evaporator.

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Old 06-09-2017, 01:32 PM   #7
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Quote:
Originally Posted by floridasl22002 View Post
You have the main control unit on the dash, which when adjusted by you instructs ..............

.............. clear but there was something not right going on in the front evaporator.
Yes it is a rather complicated system.

I've been trouble shooting only with the front HVAC controls. I turn off the rear HVAC altogether to take it out of the equation and focusing in getting the right temperature out of the front vents.

I've run all the actuators through their paces and they all seem to be functioning well. I do have one to replace in the rear system though but it can wait.

...
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Old 06-10-2017, 12:44 AM   #8
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trottida, instead of continuing here in the S-series General forums, re-post in the Other Cars forums (lest we be chased off here for discussing 'other cars'.

An initial read in the gm-trucks.com thread seems to have some questionable issues.

1-How anyone can state ac pressures get too high in winter temps to explain losing refrigerant thru the pressure relief valve is borders on perpetual motion. Basic physics and chemistry says refrigerant that's compressed generates higher pressures and temperatures. This is well known by simply feeling the discharge fitting on the compressor or inlet side of the condenser coil. They should be very hot to touch (compress a gas and its temperature rises). This scenario presumes running ac in warm weather. If winter temps are below 40F the ac system is disabled from running because its too cold out and ac effectiveness is very low. If you detect familiarity of the last sentence, it's because its the same operating principle in all Saturns and Suburbans. And most likely all GM models. I checked the service manual for suburbans. In cold weather (above 40F), ac works but discharge pressures will be lower, not higher due to physics, again. Ambient temperatures affects ac operating pressures. I suspect the mechanic is guessing and may not have a good grounding in basic refrigeration, chemistry and physics. In summer, ac operating pressures are higher due to ambient temps. In keeping with this premise, operating pressures are lower in winter due to colder ambient temps. To prove this point requires connecting refrigerant gauges in summer hot weather and when its around 45F. As to the cooling fan not operating when ac is running, it should be as simple as studying the wiring diagrams.

Presuming yours uses two cooling fans, low speed cooling runs both fans in a series circuit; 12v goes to one connection to the left fan, the other fan wire is connected thru one of three relays and connects to the right side fan with the fan grounded. This allows both fans to run at reduced speed. High speed cooling uses both fans in parallel wiring to allow full power to each fan. The ac system not running cold at low speed may be due to both cooling fans not running at all. AC demands cooling fans since the compressor generates heat.
With the condenser coil in front of the radiator, heat from the condenser coil flows back onto the radiator. If a vehicle is in local traffic. air flow is negligible so cooling fans are always turned on to maintain air flow. Without air flow thru the condenser coil, operating pressures rise higher than normal and effectively lowers cooling.

2-The comment of a leak was never found but losing refrigerant doesn't make sense. If refrigerant was lost, was the system topped off? If topped off the system lost refrigerant, period. All ac systems are sealed, no different from refrigerators that lasts for years. Unfortunately, vehicle ac systems are made using copper tubing and sit in one spot for years. Vehicle ac systems are rattled, shocked from potholes, frozen in subzero arctic temps and heated in desert weather. Heat, cold and vibration eventually attacks vehicle ac systems.

I can send service manual files if you pm me an email address that accepts files. An initial guess is the lack of both cooling fans not running when ac is turned on suggests the fan circuits, wiring, and the pcm that controls them.

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Old 06-10-2017, 07:04 AM   #9
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Thanks for your comments. I was hoping you would chime in.

I posted in a few GM and Chevy forums prior to posting here but I got impatient as I wasn't getting any feedback. I posted here and linked the one forum which seems to be getting the most reads. I thought the conversation would take place on the GM forum. I have a lot of trust in the membership here and I know that I would get some help.

Regarding the pressure relief statement; I called BS on that one and subtly reflected that with a question mark after my statement. I did not know for sure so I thought it was important to mention it.

The system does use 2 fans, they are electric and they can be turned on using a scanner so we know they are working. For some reason the PCM is not sending the command to turn them on. The scanner pointed to the temp control module in the dash as when the AC switch is pressed the command goes to the PCM and then is promptly cancelled. I replaced that controller and there was no change but I have yet to see what the scanner says.

I appreciate you sending the GM files, that will be helpful for me understanding all the possible variables. I may come back to your post later as I'm limited to reading and replying on my phone.




Quote:
Originally Posted by fdryer View Post
trottida, instead of continuing here in the S-series General forums, re-post in the Other Cars forums (lest we be chased off here for discussing 'other cars'.

An initial read in the gm-trucks.com thread seems to have some questionable issues.

1-How anyone can state ac pressures get too high in winter temps to explain losing refrigerant thru the pressure relief valve is borders on perpetual motion. Basic physics and chemistry says refrigerant that's compressed generates higher pressures and temperatures. This is well known by simply feeling the discharge fitting on the compressor or inlet side of the condenser coil. They should be very hot to touch (compress a gas and its temperature rises). This scenario presumes running ac in warm weather. If winter temps are below 40F the ac system is disabled from running because its too cold out and ac effectiveness is very low. If you detect familiarity of the last sentence, it's because its the same operating principle in all Saturns and Suburbans. And most likely all GM models. I checked the service manual for suburbans. In cold weather (above 40F), ac works but discharge pressures will be lower, not higher due to physics, again. Ambient temperatures affects ac operating pressures. I suspect the mechanic is guessing and may not have a good grounding in basic refrigeration, chemistry and physics. In summer, ac operating pressures are higher due to ambient temps. In keeping with this premise, operating pressures are lower in winter due to colder ambient temps. To prove this point requires connecting refrigerant gauges in summer hot weather and when its around 45F. As to the cooling fan not operating when ac is running, it should be as simple as studying the wiring diagrams.

Presuming yours uses two cooling fans, low speed cooling runs both fans in a series circuit; 12v goes to one connection to the left fan, the other fan wire is connected thru one of three relays and connects to the right side fan with the fan grounded. This allows both fans to run at reduced speed. High speed cooling uses both fans in parallel wiring to allow full power to each fan. The ac system not running cold at low speed may be due to both cooling fans not running at all. AC demands cooling fans since the compressor generates heat.
With the condenser coil in front of the radiator, heat from the condenser coil flows back onto the radiator. If a vehicle is in local traffic. air flow is negligible so cooling fans are always turned on to maintain air flow. Without air flow thru the condenser coil, operating pressures rise higher than normal and effectively lowers cooling.

2-The comment of a leak was never found but losing refrigerant doesn't make sense. If refrigerant was lost, was the system topped off? If topped off the system lost refrigerant, period. All ac systems are sealed, no different from refrigerators that lasts for years. Unfortunately, vehicle ac systems are made using copper tubing and sit in one spot for years. Vehicle ac systems are rattled, shocked from potholes, frozen in subzero arctic temps and heated in desert weather. Heat, cold and vibration eventually attacks vehicle ac systems.

I can send service manual files if you pm me an email address that accepts files. An initial guess is the lack of both cooling fans not running when ac is turned on suggests the fan circuits, wiring, and the pcm that controls them.

...
Current rides
2001 SL1 MT (410,500 km @ 11/2017)
1999 SL2 MT (251,500 km @ 11/2017)
2011 Suburban LT (101,450 km @ 11/2017)

:canada:

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Old 06-11-2017, 08:17 PM   #10
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trottida, ........Unfortunately, vehicle ac systems are made using copper tubing and sit in one spot for years. Vehicle ac systems are rattled, shocked from potholes, frozen in subzero arctic temps and heated in desert weather. Heat, cold and vibration eventually attacks vehicle ac systems. ....
A correction is needed. Vehicle ac systems are made using aluminum, not copper. Copper is used is home refrigerators.

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Old 06-12-2017, 06:45 PM   #11
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Hmm, so the refrigerant pressure relief valve is a thing apparently ....

Quote:
The A/C system is mechanically protected with the use of a high pressure relief valve. If the A/C refrigerant pressure sensor were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.
So there is a possibility of the system discharging refrigerant in a high pressure situation.

Still reading documents Fdryer emailed me ....

...
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Old 06-12-2017, 08:16 PM   #12
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For Suburbans;

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables the compressor clutch if the A/C pressure is more than 2957 kPa (429 psi). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi).

A/C Low Pressure Switch
The A/C low pressure switch protects the A/C system from a low pressure condition that could damage the A/C compressor or cause evaporator icing. The HVAC control module applies 12 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 124 kPa (18 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40 psi). This enables the A/C compressor to turn back ON.

The A/C system is mechanically protected with the use of a high pressure relief valve. If the A/C refrigerant pressure sensor were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.


I can't find specs on Suburban compressor relief valves. Knowing the electronic pressure sensor detects up to 429 psi to disable compressor operation, the mechanical pressure relief valve mounted on the compressor has to operate at a higher pressure (455 psi?). Vues have their relief valves set to release between 575-490 psi, resetting around 425 psi. When a relief valve blows off excessively high pressures, service manuals recommend replacing it. I would imagine Suburban relief valves are set somewhere in the same range but above the electronic pressure sensor (429 psi) to preclude interference between them.

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Old 06-12-2017, 08:33 PM   #13
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Default Re: Looking for a GM Tech/Specialist

Quote:
Originally Posted by fdryer View Post
For Suburbans;

The A/C refrigerant pressure sensor protects the A/C system from operating when an excessively high pressure condition exists. The PCM disables the compressor clutch if the A/C pressure is more than 2957 kPa (429 psi). The clutch will be enabled after the pressure decreases to less than 1578 kPa (229 psi).

A/C Low Pressure Switch
The A/C low pressure switch protects the A/C system from a low pressure condition that could damage the A/C compressor or cause evaporator icing. The HVAC control module applies 12 volts to the A/C low pressure switch signal circuit. The switch will open when the A/C low side pressure reaches 124 kPa (18 psi). This prevents the A/C compressor from operating. The switch will then close when A/C low pressure side reaches 275 kPa (40 psi). This enables the A/C compressor to turn back ON.

The A/C system is mechanically protected with the use of a high pressure relief valve. If the A/C refrigerant pressure sensor were to fail or if the refrigerant system becomes restricted and refrigerant pressure continued to rise, the high pressure relief will pop open and release refrigerant from the system.


I can't find specs on Suburban compressor relief valves. Knowing the electronic pressure sensor detects up to 429 psi to disable compressor operation, the mechanical pressure relief valve mounted on the compressor has to operate at a higher pressure (455 psi?). Vues have their relief valves set to release between 575-490 psi, resetting around 425 psi. When a relief valve blows off excessively high pressures, service manuals recommend replacing it. I would imagine Suburban relief valves are set somewhere in the same range but above the electronic pressure sensor (429 psi) to preclude interference between them.
I was reading a bit about the low pressure switch and noted that it feeds data into the HVAC Controller Module; could it be faulty and be shutting the system down at the lower RPM's. I see that it requires a special tool to test it.

Too low RPM's would also shut the system down but I don't seem to have idle issues; the engine runs fine.

...
Current rides
2001 SL1 MT (410,500 km @ 11/2017)
1999 SL2 MT (251,500 km @ 11/2017)
2011 Suburban LT (101,450 km @ 11/2017)

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Old 06-12-2017, 09:23 PM   #14
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Default Re: Looking for a GM Tech/Specialist

As technical as the service manuals are, a lot of it must be viewed from a different perspective. That perspective comes from experience and time spent working on vehicle ac systems. I am not an expert on vehicle ac systems but have worked on basic r12 systems back in the '70's with a simple thermostatic control on the temperature lever to control compressor operation; selecting ac and setting the temperature selector to between cold and hot; sets the damper fro the amount of heat needed (free from hot engine coolant) and thermostatically controlling compressor operation to maximize heat and cold air into the car. Fast forward to my L300 with auto climate control that does essentially the same thing but doesn't shut off compressor operation. The compressor has its own temperature/pressure sensor to vary displacement so local stop and go would mean low speeds a but requiring higher output from the compressor to maintain a 'banked' supply of liquid refrigerant so the thermal expansion valve can supply as much low pressure refrigerant to absorb heat from the interior. As speed increases, efficiency increases and the compressor output less volume while the interior stays at selected temperature. Old r12 compressors had straight displacement and presented operating problems as I saw many various methods of controlling cold. The engine area was stuffed with many mechanical devices to modulate the liquid supply to the evaporator coils. A nightmare I didn't have to deal with and took it on faith that they never failed when...............the majority of system problems were as it is now, the leak no one wants to address while everyone jumps to conclusions about this and that failure. To this day, compressors are blamed for failure when they're not. They're simply the fall guy for the misinformed, misled, clueless, inept, and any other adjective to describe anyone, including so called ac mechanics/technicians that would have anyone believing compressors fail all the time. Compressors are the largest profit makers so its understandable from either the dealer or repair shop. Personally, only one compressor failed in my limited experience and it actually didn't fail so much as the rubber flex coupling used deteriorated to the point that the coupler disintegrated, failing to engage when the clutch coil powered up. If i had the tools to replace the clutch assembly, I would have reused a perfectly good compressor. The car was driven another year before donating it. All my repairs are 100% leaks from damaged condenser coils, crimped fittings wearing out, chafed tubing rupturing, and poor male/female mating surfaces. All leaks. Compressor remains original and in working condition with all the procedures followed to ensure restoration to factory condition. Nothing I do is exceptional because anyone can do the same if time, skills and knowledge are used.

Without investigating how Suburban ac system operate, even a dual front/rear ac system, I tend to separate ac problems into two areas; the actual sealed system and the electric/electronic controls, known as the head unit, hvac control unit/head, whatever. Even with more electronic sensors placed everywhere on the plumbing system to monitor temperatures and pressures, the majority, if not all of them, are reliable to the point of ignoring them. I try for simplicity once I can understand the overall operating perspective. While it does take some time on my part to learn about the overall operating perspective, this also allows me to sometimes 'shotgun' an answer, skipping many things that are distractions. Sensors are distractions to the overall ac system. Either a sealed system is operating correctly or not. The diagnosing of 'or not' is determining whether the system lost refrigerant (LEAK) and creating a cascade effect of errant sensors or something actually failed and creating an unusual condition. I go for the simple stuff first before becoming entrenched in sensor failure(s). It also helps to find out if there are any service bulletins that informs dealers of specific problems and whether or not a recall is needed. Service bulletins are not the sole property of GM as we all own our vehicles with any service bulletins pertinent to warranty or out of warranty, safety issues or running changes that address recurring problems.

To sum it all up, either the ac system is sealed or not and the only way to know this is with gauges and service manual temperature/pressure charts or using a uv light to search the entire ac plumbing system for dye markers, pointing to the leak that's causing loss of cooling. This presumes the cabin filter, if used, was replaced and not blocking air flow from years of neglect (one or two members have done this, ignoring owner's manuals to replace cabin filters and concluding ac failure...) Electronics can only do their job if the sealed system remains sealed. Once a leak occurs, no matter how small or large, the hvac electronics may have a 'field day' with incorrect inputs to to hvac control head and appear as an electronics problem. Electronics tends to be reliable against soft aluminum plumbing of vehicle ac systems that have a history of break downs. My faulty ac system is no different from millions of other ac systems with wear and tear breaking plumbing to cause a perfectly sealed system to become unsealed, leading to loss of cooling. Once repaired and sealed again, everything works.

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Old 06-15-2017, 07:33 AM   #15
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Default Re: Looking for a GM Tech/Specialist

Well it doesn't seem to be the Suburban's AC Control Module. It's all programmed with the latest updates from GM and the AC is still not cooling at idle. Heat seems to be working well again and now at least I don't have to replace some burned out bulbs in the old module.

The thought now is perhaps the AC Compressor is tired. Works fine with higher RPM's but as soon as it hits idle it stops cooling. Mechanic is pretty confident that there are no system blockages; he checked the orifice tube and it was clean. The known history indicates no catastrophic failures that would cause blockages. History includes leak in rear AC line which was replaced and a leak in the rear evaporator core which was also replaced.

They looked for a used compressor locally and there are none to be had in this area. New compressors are surprisingly not that expensive. I'm not sure where I'm going to go from here.

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Old 06-15-2017, 08:07 AM   #16
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Default Re: Looking for a GM Tech/Specialist

You can measure the suction and discharge pressures and temperatures at idle which will tell you the mechanical condition of the compressor. Has this been done? Usually a shop job to have the test data available.

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Old 06-15-2017, 09:01 AM   #17
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Default Re: Looking for a GM Tech/Specialist

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Originally Posted by OldNuc View Post
You can measure the suction and discharge pressures and temperatures at idle which will tell you the mechanical condition of the compressor. Has this been done? Usually a shop job to have the test data available.
I'm told that the pressure readings are in spec but I don't have them. They've had the truck for 3 days while I was away and can't come up with a reason for it's poor performance at low rpm.

I'm suspicious of the low pressure switch from what I've seen in the schematics. It communicates directly with the HVAC Control Module. I'm going to question them again about it. I'll see if I can get the pressure readings.

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Old 06-15-2017, 09:23 AM   #18
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Default Re: Looking for a GM Tech/Specialist

One of the common issues with some, or all, R-134a systems is a complete failure of the system at idle. This is usually corrected with an axillary electric fan to increase the condenser air flow. Common problem in the warmer and higher humidity parts of the US. Most common in the basic orifice tube systems.

Generally the quick test of this theory is to place a common household box fan in front of the vehicle and put on highest sped and then run the vehicle at idle only with the A/C on max cool. If the A/C functions as expected, cools the vehicle, then you have identified the problem.

A defective LP switch will also cause problems but that should be obvious from pressure readings as the LP switch setpoint is not top secret information and if is tripping prematurely the tech should spot that easily.

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Old 06-15-2017, 10:02 AM   #19
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Default Re: Looking for a GM Tech/Specialist

Quote:
Originally Posted by OldNuc View Post
One of the common issues with some, or all, R-134a systems is a complete failure of the system at idle. This is usually corrected with an axillary electric fan to increase the condenser air flow. Common problem in the warmer and higher humidity parts of the US. Most common in the basic orifice tube systems.

Generally the quick test of this theory is to place a common household box fan in front of the vehicle and put on highest sped and then run the vehicle at idle only with the A/C on max cool. If the A/C functions as expected, cools the vehicle, then you have identified the problem.
There are 2 electric fans in the system, one for cooling and the other for the AC Condenser. The condenser fan is working but the compressor is not turning on at low RPM's so the fan does not turn on. The cooling is fine with higher RPM's.



Quote:
A defective LP switch will also cause problems but that should be obvious from pressure readings as the LP switch setpoint is not top secret information and if is tripping prematurely the tech should spot that easily.
To test the LP switch requires a special tool (Kent Moore Special Tool GE*47742); not sure an independent shop would have one or not. See document attached. Basically you remove the LP switch, attach it to the tool and then attach the tool to the LP switch port.
Attached Files
File Type: pdf Info - Diagnostic Information.pdf (113.3 KB, 1 views)

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Old 06-15-2017, 10:15 AM   #20
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Default Re: Looking for a GM Tech/Specialist

Try the external fan test. If that gets the installed fan to switch on then you can point at the LP switch as having an elevated trip setpoint.

Special tool not required to bench test pressure switch. Problem is what is required is not common repair shop or dealer equipment.

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