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Old 06-23-2017, 08:10 AM   #41
OldNuc
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Default Re: Looking for a GM Tech/Specialist

There is nothing like poorly designed complexity to run up maintenance and repair costs.

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Old 07-04-2017, 07:01 AM   #42
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Default Re: Looking for a GM Tech/Specialist

Just a followup...

The AC Compressor, receiver dryer, orifice tube, AC belt and AC belt tensioner were replaced and while I think it is working marginally better at idle, we haven't had any decent weather to stress test it yet.

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Old 07-05-2017, 11:28 AM   #43
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So we had 27 C weather yesterday (according to the ambient temp sensor) and I was able to stress test the AC System at 32% humidity. At idle the front center vents (driver and passenger) were blowing 27C whereas the front left AUX AC vent was blowing 20C. When I increased the RPM's to 3K the front center vent dropped down to 22C. I'd say that there is still something going on. Not sure where to go from here but because the condenser is working for the rear AC I wouldn't think that was suspect. The only other thing it could be is the front evaporator. What does everyone think?

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Old 07-05-2017, 11:43 AM   #44
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Default Re: Looking for a GM Tech/Specialist

Can you get to the inlet and outlet of the evaporator, basically the actual core inlet and outlet? If so measure the temperature differential across the evap. This may be internal bypass leakage in the HVAC box.

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Old 07-05-2017, 11:46 AM   #45
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Default Re: Looking for a GM Tech/Specialist

Quote:
Originally Posted by OldNuc View Post
Can you get to the inlet and outlet of the evaporator, basically the actual core inlet and outlet? If so measure the temperature differential across the evap. This may be internal bypass leakage in the HVAC box.
Hmm, not sure, I'll have to check. What should I expect the temperatures to be if working correctly?

...
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Old 07-05-2017, 01:58 PM   #46
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Default Re: Looking for a GM Tech/Specialist

At 27C/81F and 32% humidity, what were operating pressures? Service manuals refer to idle rpm for measuring operating pressures to select which zone containing a check list.

Do both cooling fans run with ac on? Be aware that cooling fan operation depends on coolant temps and/or ac operation. Both fans turn on at low speed with coolant above 94.5C/202F or ac pressures above 210 psi.

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Old 07-06-2017, 06:49 AM   #47
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Default Re: Looking for a GM Tech/Specialist

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At 27C/81F and 32% humidity, what were operating pressures? Service manuals refer to idle rpm for measuring operating pressures to select which zone containing a check list.

Do both cooling fans run with ac on? Be aware that cooling fan operation depends on coolant temps and/or ac operation. Both fans turn on at low speed with coolant above 94.5C/202F or ac pressures above 210 psi.
I didn't get the new numbers from the mechanic for operating pressures after the compressor and other components were replaced. I also hadn't rechecked what the fans are doing at idle but prior to replacing the compressor they were shutting down shortly after letting the engine idle. I'll see if I can get some more information this evening.

So at idle would you expect AC pressures to drop below 210psi and the fans to shut down?

...
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Old 07-06-2017, 08:30 AM   #48
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Default Re: Looking for a GM Tech/Specialist

As a general matter those fans should run at idle.

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Old 07-06-2017, 03:54 PM   #49
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Default Re: Looking for a GM Tech/Specialist

Quote:
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I didn't get the new numbers from the mechanic for operating pressures after the compressor and other components were replaced. I also hadn't rechecked what the fans are doing at idle but prior to replacing the compressor they were shutting down shortly after letting the engine idle. I'll see if I can get some more information this evening.

So at idle would you expect AC pressures to drop below 210psi and the fans to shut down?
That question is difficult to answer as the service manual does not state cooling fans turning on when ac is used. Its easy for anyone to say yes it does but I try to use service manuals for these technical questions. It may very well be less than 210 psi is your operating pressure at idle. As mentioned previously, Suburbans turn on cooling fans when ac operating pressures are above 210 psi or coolant temps above 94.5C/202F. I realize this becomes a tedious and time consuming check but that's part of any technical issues when trying to determine why ac cooling doesn't occur at idle/low speed until rpm run above idle (high side operating pressures increase in direct proportion to engine rpm). I use all pertinent info and not hearsay to discern what should be (service manual specs) and what's observed with gauges and temperatures. My experience has always been with ac and cooling fans running simultaneously. Unfortunately, not here with Suburbans. What makes this model stand apart from my limited exposure of vehicle ac systems are the numerous temperature sensors, using an orifice tube on the main hvac evaporator coils with txv on the rear hvac evap coils, and operating pressures/temperatures to turn on both cooling fans. Large air conditioners (the ones custom sleeved to fit into openings in homes) with capacity around 18k-30k BTUs use the same basic capillary tube as small units, including every size home freezer or refrigerator. A simple small diameter capillary tube serves as the separation between high pressure liquid refrigerant and the evaporator coils instead of a complex thermal expansion valve. Basic room ac units, refrigerators and freezers haven't changed in decades, just better mechanical designs in efficient pumping, better motors and environmentally friendly refrigerants.

Since I don't know exactly what are typical operating pressures in real world operation of Suburbans and can use the temperature/pressure charts, it would be too easy to state operating pressures exceed 210 psi and the cooling fans are on. In reality, operating pressures vary a lot and in proportion to outside temps - lower when temps are around 16C/61F, higher when around 37C/100F. To make any assessments, I would have gauges connected and note low and high side pressures@idle rpm, ambient temps, vent temps and whether or not both cooling fans are running. And service manual info on hand. I would be doing no less than is expected of good repair shops equipped with much more access to equipment, tools and information. Discussing a topic like refrigeration is one thing, performing diagnostics is another and sometimes not the same with many not informed enough to differentiate between talking the talk and walking the walk where they should be the same. Misinformation and misleading info from hearsay oftens interferes with online discussions. To eliminate misinformation, I try to use manuals for specific references and ask specific questions. If I had to make armchair quarterback guesses, I wouldn't comment at all.

BTW, engine ".....with engine cooling fan..." means the engine cooling fans are running to force airflow in service bays instead of an external electric fan placed in front of a vehicle during diagnostics.

Using the temperature/pressure charts, fans should be running in the green zones or minimum 30C/86F, higher than 30% humidity. The boxed zones show fans should be running in the 'A' zone with a minimum low side pressure just below 20 psi and high side pressure at 210 psi. Where these two values coincide would be using the temperature/pressure chart.

My guess is suspecting the orifice tube is incorrect (presuming full refrigerant amount and pressures are within range). There are different sized orifice tubes specified for each model. Orifice tubes separate the high pressure liquid line from the low pressure gas state in evaporator coils. No different from small diameter copper capillary tubes used in home refrigerators and room ac units. The specific inside diameter controls refrigerant liquid flow to allow a liquid to flash into gas where the expansion of liquid refrigerant absorbs heat from the internal surfaces of the evap coils. To make a limited educated guess, a larger diameter orifice tube incorrectly used may release too much refrigerant and not allow idle rpm cooling while higher rpm creates more suction pressure to remove gases and allow refrigerant to work better. The correct orifice tube (smaller diameter in comparison to an incorrect larger diameter tube) should release refrigerant at the correct flow rate to allow gas expansion while absorbing heat. Using orifice tubes has its own limited range and may be the reason its not used in regular cars and most suvs. Every design has built in compromises and I don't know why its used in the front hvac box. In theory, the appropriate orifice tube may create icing conditions where the various temperature sensors detect it to tell the ecm of impending icing and cycle the compressor off to allow evaporator temps to return above freezing. An incorrect orifice tube would throw off the correct operating pressures, resulting in warm temps at idle and may explain why you said fans didn't turn on when ac is running at idle. There are many issues that can occur with strange symptoms if incorrect parts are used........
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Last edited by fdryer; 07-06-2017 at 04:03 PM..

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Old 11-02-2017, 08:22 AM   #50
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Default Re: Looking for a GM Tech/Specialist

Just to close this off; the new ACDelco compressor worked for a few weeks and then the compressor seals blew. We replaced the part under warranty and had it installed and then the high pressure relief valve discharged the system after a couple weeks.

Finally, after a couple days of intermittent testing and head scratching they replaced the pressure sensors even though they tested good and that is where we left it.

At the beginning of October we bought a 2011 Suburban LT and sold the 2005 Suburban the day after the pressure sensors were replaced in mid October. I'll never really know if it was 100% resolved but the A/C was working when we delivered it to the new owner.

...
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Old 11-03-2017, 09:22 AM   #51
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Default Re: Looking for a GM Tech/Specialist

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Old 11-03-2017, 12:11 PM   #52
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Default Re: Looking for a GM Tech/Specialist

Now all you have to worry about is the dashboard top fracture cracking in multiple places!

It's a well known issue on the last version of the Suburban (the one you just bought). GM know about it but don't seem to be doing anything about a recall. At around $700.00 just for the top plus fitting, it is not a cheap issue. Google it.

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