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Old 04-01-2013, 03:22 PM   #1
TurboZutek
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2003 L-Series 2.2L Sedan
Default Air Conditioning Oddity

Hey everyone!

Today I was replacing the coolant on my 2003 L200 (2.2) and it all went very well. Draincock opened up nicely, everything drained out good, splendid!

One thing of concern I did notice when I was bleeding the system afterwards was that the AC pump would run at odd times. I understand the AC should come on with the demist function for the front screen (when the dial is all the way to the right), but the pump was firing up when the control was set to ANYTHING at all on the right hand side.

Face vents only (dial all the way left) = AC off
Bottom and face vents = AC off
Hitting the middle of the dial = AC pump ON and spinning.
Bottom only = AC ON and spinning.
Both screen vent positions (dial to the right) = AC ON and spinning.

WTF? Has anyone else seen this? Is this normal behaviour? Why?

How much gas have I wasted over the years by running the AC when I don't want it?

Any thoughts guys and girls?

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Old 04-01-2013, 06:54 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: Air Conditioning Oddity

Are you sure the compressor is actually running, creating cold air or is it just spinning without making cold air? One of two ways to tell would be to select/dial 'C' on the temperature knob on low/medium fan speed in face vent mode. It will have to be warm outside to notice if the compressor is running (presuming a/c is in good working condition) and making cold air or if outside air isn't conditioned. The other way to tell if the compressor is running is the a/c indicator and compressor clutch engaging with a distinctive loud click as the clutch is energized. If the a/c button/indicator isn't pressed ON then only outside air should be felt. I don't know if your controls defaults to a/c mode when turning on the blower. Auto climate controls like mine in L300's defaults to a/c mode when manually turning on the HVAC system. Pressing the A/C OFF button will disable the compressor for normal blower and temperature use unless selecting defrost. My guess is that 'upscale' L300 owners prefers auto a/c continuously, selecting 'auto' fan control and dialing in a temperature for total auto climate control without ever touching the HVAC controls again. I'm not an 'upscale' L300 owner and prefer how cold/hot I want and when I want a/c cooling.

If a/c is running erratically in several modes not desired then it may be a control head issue. Can you manually turn off a/c when not in defrost mode?

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Old 04-01-2013, 11:08 PM   #3
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2003 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

Thanks for reading and replying!

I should have mentioned; the AC control on this car is manual. By default (as far as I'm aware) the only way the AC should power up is if the AC button is pressed, or the control is moved to the 'FULL DEMIST' pictograph on the far right/bottom. Here's what I get:



Everything that's marked in blue here seems to fire up the AC in that:

You can see the AC clutch spinning when it's in the blue section of the controls, when you switch over to anything on the other side, the centre boss of the AC clutch assembly loses speed and stops.

Currently it's not too easy to take temperature readings from the vents because it's wet and cold, but the pipework from the AC compressor DOES get cold one side and hot the other, which tells me the compressor is, well, compressing!

I think the whole 'auto AC with demist' is a pain in the neck, but this is an even bigger headache if it's going to do it on half of all settings!

Chris...
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Old 04-02-2013, 12:46 AM   #4
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2000 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

A couple of months ago, or so, I discovered the same issue with my car. Your HVAC controls and mine are identical. It turned at that the a/c would engage at a point slightly before or at the location of the floor vents only (no mix of upper vents) regardless of whether or not the a/c switch was "on." After the engine was fully warm I checked the RPM to note any increase as I moved the vent selector dial toward the right (clockwise) from the upper vents only point (bottom left of the dial settings).

Voila! There it was; just as I reached a detent point at or near the floor vents the RPM jumped - perhaps fifty to seventy five RPM higher than at normal idle. From that point further toward full defrost vent usage the a/c compressor was always engaged. Frankly, I don't like that kind of set up, but that's what we've been provided with. In So. California I don't need a compressor on every time I use the floor and/or defrost vents. The net result of that to me was a noticeable drop in fuel economy for having used those vent selector positions - very annoying.

What was my choice then? I wouldn't use any of the vents which would automatically engage the compressor unless I absolutely had to.

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Old 04-02-2013, 12:52 AM   #5
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2003 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

That is just... Bizzaro. There are some really stupid design choices on this car but this one takes the cake.

Ok, this month sometime I'm going to pull that panel apart and find out why it does what it does and how to stop it. I'd like to bring the AC back to being tied to the AC switch and nothing else, period. I'll remember to run the AC for 10 mins a week manually myself.

Thank you for posting pierrot, I don't feel like I'm crazy and alone anymore, lol!

Chris...

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Old 04-06-2013, 05:40 PM   #6
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2003 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

Right, buttocks, here goes!

I stripped down the AC controller and I found this:



The good old Haynes manual helpfully got the wiring WRONG, but I managed to work out that voltage is sent to the BCM for AC from this connection:



Which is driven from two diodes, one which connects to the AC switch, the other that connects to the logic IC. I'm going to remove the logic IC diode in the hope that it will no longer supply power to the BCM and trigger AC.

I'll keep you posted.
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Old 04-06-2013, 06:51 PM   #7
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2003 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

Right, great news everyone:

My car only switches the AC on .. WHEN I PRESS THE SWITCH!! Ding dong, the fuel robbing witch is dead!! Ok, so it's a really easy mod to do, though it took some time tracing circuits and figuring out (WTF).

Dig into the AC control unit until you get the PCB out:



Then simply take your soldering iron, or pair of snips and remove the lower of the two diodes above the selector potentiometer:



Hurrah, simple as that. Button it all up again and you're done. Don't forget to run your AC for 10 mins a week EVERY WEEK after performing this mod!

How it all works:

This solid state design of PCB that we have here basically takes the value of the potentiometer and from the resistance calculates where the knob is pointed. From that, it uses the higher resistances (rightmost side) to work out when the AC should be on. This is a lazy and less accurate design, but cheaper to make as all you need is a commonly available comparator and some resistors. It also means the car wiring can be as similar as possible between auto and manual climate control units, saving more money for GM.

Anyway, once it works out the AC should be on, it feeds this value to a pin on the right sided IC which powers the diode we just removed. This pin is now defunct in the design and feeds nothing. The diode we left behind here is the one connected to the manual switch, so we will keep that one, though if you wanted to disable AC completely for some reason, you could remove it also.

Chris...
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File Type: jpg The Logic PCB Neutered.jpg (112.8 KB, 71 views)

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Old 04-15-2013, 10:44 PM   #8
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2003 L-Series 2.2L Sedan
Default Re: Air Conditioning Oddity

And I'm happy to report the first full tank has returned 21.5 extra Kilometres since this mod.

Fuel economy WIN!

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Old 04-16-2013, 12:37 AM   #9
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2003 L-Series 3.0L Sedan
Default Re: Air Conditioning Oddity

Outstanding! This is right at the top of must do mods.

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