A thank you, and a question

[izzie]

I've owned my 05 LS V8 for a couple years now, and this forum has been very useful in diagnosis and repair. Thank you to those who have posted this valuable information. My latest job was all eight COPs, although I'm still a novice everything went smoothly... mostly.

My question is in regard to AC. I've searched and read a bunch. Self diagnostic on the hvac panel gave me 2 codes. One for a shorted evap discharge sensor. Unplugged it, code changed to open, replaced it, code is gone. AC still doesn't work. Other code is 12 65 which I'm told I can ignore as this model does not have a blend door.

Check DCCV. Clamped off one of the three hoses near dccv, still no AC. Clamped off a different hose near heater core, no love. DCCV is still in question, but not likely to be the only culprit if it has failed. I already bought one since the damn thing sounds like a time bomb. AC blows hot when the engine is hot. If it's in the garage with the hood open, blows ambient air.

Pretty simple, does the compressor kick on? I don't hear it. Check 10a fuse under hood, looks good, replace it any way. Swapped the relay with another that I know to be good. Nothing.

I checked the low side port but that's been a couple years ago, pressure was good. Short the pressure switch and see if it kicks on? I'm not sure where that is. Also I'd like to touch one of the refrigerant lines to see if it's cooling, but are there any I can reach in the engine bay without pulling off the front drivers wheel?

I'm assuming refrigerant pressure, clutch, compressor in that order of diagnosis. Still a newbie so treat me like I'm very very stupid.

 

[joegr]

You have to clamp off at least two of the three heater core hoses to be sure...
Anyway, look at the center part of the AC pulley. If it's not turning, the clutch is not engaged. It's probably not engaged due to low refrigerant pressure. The system looks at high side pressure, not low side. It has to be fairly high for it to start (well above the "normal' range on those cheap low side fill-kit/gauges). I believe that you can unplug the connector to the high side pressure switch to bypass it (nothing to short), but I wouldn't do that. You can do a lot of system damage in a few seconds, depending on what has happened.
The most common AC leak that I have seen is at the compressor. When it leaks there, all the oil leaks out before the refrigerant. If the compressor runs without oil, it could destroy the expansion valve as well as the compressor. You have to take the whole dash out to replace the expansion valve.

 

[izzie]

Was able to get our fleet mechanic at work to check the system with his gauges, system was/is fully charged. Hit it with a voltmeter while I was down there and power doesn't seem to be an issue. I believe that I'm left with either clutch or compressor. Any other options before I pay for a replacement?

 

[elephantrider]

for what its worth, when the ac was out on mine, it was the ac manifold leaking.
sounds like you have a full system though, so i'd lean toward the compressor
being ill.

 

[joegr]

Was able to get our fleet mechanic at work to check the system with his gauges, system was/is fully charged. Hit it with a voltmeter while I was down there and power doesn't seem to be an issue. I believe that I'm left with either clutch or compressor. Any other options before I pay for a replacement?

I don't understand. There's no way to verify that the charge is correct without the compressor running. So which is it?

1. Clutch engaged and compressor ran. After a few minutes of stabilization, the low and high side pressures correctly matched the chart for the temperature at the time. The fan was on high.
- Either everything's fine or you got very hot air out and most likely your DCCV is failed.

-or-

2. The clutch did not engage and the compressor did not run. He was unable to verify the high and low side pressures (since it wasn't running) and he does not know if it is correctly charged or not.

Please explain if it is not one of these two possibilities...

 

[izzie]

The answer is door number two. Since the compressor never kicked on, we aren't able to verify a correct charge. There are only so many potential failure points that would prevent the clutch from engaging. Does it matter that the compressor never turned on if we're trying to eliminate high side pressure sensor as the cause? I'm trying to do my due diligence before compressor replacement, is there anything left to check?

 

[joegr]

The high side sensor will keep the compressor from starting if the high side pressure is too low or too high. The evaporator temperature sensor will keep the compressor off if it thinks the evap temperature is below freezing. The PCM will keep the compressor off if the engine is overheating or idling to low. Also, there is a thermal fuse/switch on the side of the compressor at the back.