QuestionHello,
I have a 05 Avalanche and the AC work poorly. It does blow cool air but it seems to be between 65-70 Deg F. I checked the pressures and it seems the the low side is about 70-80psi and the high side seemed low based on the outside temp at around 190-200psi on a day with outside temp of over 95deg F. (When I checked the pressure, I had a big fan in front of the condenser to make sure I had proper air flow.)When I brought up the engine RPM it did not get any cooler and the pressures stayed about the same (slight change)I do not believe this is a blend door issue as the suction side pressure is pretty close to the cab temperature that I would expect for 70-80n psi(measured with a thermometer placed in the center duct with the AC on max cool).
It would seem that this would be a compressor issue but I am not too sure because the clutch style on this car is different to what I am used to seeing. The clutch does not turn on and off like a normal clutch. It seems to be always engaged. I am not too familiar with this type and I was wondering if you could tell me if this clutch function is normal and how it works. Other than changing the compressor do you have any other suggestions of how I can get my pressures down on the low side and higher on the high side.
Thank for your help.
Robert
AnswerRobert,
Thank you for the very detailed question. It is rare that I receive one on here that tells me everything I need to know, and I do appreciate it.
Ok, if your A/C is blowing out 65 degrees on a 95 degree day, it is working exactly as it is designed to. The A/C systems are only designed to drop the temperature of the confined space 30-40 degrees from the outside ambient temperature. A little story on that... during my last tour in Iraq, there were many vehicles being brought into my shop because they were blowing 85-ish degrees out of the vents. But with the outside temp at 120+, They were working perfectly.
From the information you gave me... that backs up the answer being nothing wrong. On a 95 degree day your high side will read in the area of 183psig on the high side and 58 on the low side. You said that the temp was over 95 degrees, so that works out that the pressures will read slightly higher.
How to figure this... on a 95 degree day...
High side= Ambient temperature (95)+30(temp. difference for a forced convection condensor) = 125deg. fahrenheit. Then take this number a reference it to a pressure/temperature relationship chart for R134a (here is a link to a fair one... http://www.csgnetwork.com/r134apresstempconv.html
and that number is what your pressure should read.
For the low side it is figured by subtracting 35 from the ambient temperature. (35 is the temp. difference for a forced convection evaporator) Then again... reference it to a pressure/temperature chart.
As for your clutch not disengaging... On max A/C, it will not disengage because it is trying to get the cab as cool as it possibly can. On any other setting, it will disengage only when your cab temperature sensor or thermostat says that the cab has been cooled to the temperature you have it set for. Now if you mean that it will not turn off even if you turn the a/c control off, then yes you have a problem there. Unless you have it set for defrost... if you set your control to defrost, this will also engage your clutch (this presvents the shaft seal from drying out and leaking during the winter months when the A/C isn't being used) If yours is engaged even when you tell it to turn off, le tme know, I will gladly work with you through your wiring to hopefully find the problem.
Thank you for your question, I hope I was of some assistance. If I can do more to assist either now or in the future, please do not hesitate to ask. If you found this answer at all helpful, please remember to rate this answer. Thanks again and good luck in everything.
