05 Uplander ac question

[pcabn]

So today the ac not working quite right. It keeps turning on and off. Sometimes cold other times not. Not sure if this means low freon or what to look for. No codes are in the system currently.

[gmtech1]

Originally Posted by pcabn

So today the ac not working quite right. It keeps turning on and off. Sometimes cold other times not. Not sure if this means low freon or what to look for. No codes are in the system currently.

You may have a low charge. Need to have the pressures checked with low AND high side pressures. You could also have a qualified shop recover the system and verify the proper charge. If its low, the leak will need to be found and repaired.

[brcidd]

That system does not cycle on low charge- uses a temp sensor to cycle- not a pressure switch.

are your cooling fans working? a compressor thst turns on and off may be due to high pressure cut-outs due to no air flow across condenser due to cooling fans inop.......

report back

[Tech II]

I disagree....it does not have a temp sensor, it has a pressure sensor(this is not like a pressure cycling switch, it CAN'T be jumped)......either low on freon or your have a pressure sensor/PCM/wiring/relay problem.....would need a scan tool to read what the PCM is seeing from this sensor while the system runs....if not available, then like GMTech1 says, need a set of gauges on this while it is running....it's also possible a code is set....however, if I remember correctly, if a code is set, the PCM disables the compressor, but this is not the case....

[brcidd]

Originally Posted by Tech II

I disagree....it does not have a temp sensor, it has a pressure sensor..

I disagree- .it has both

So if there is NO temp sensor as you say- how does the system avoid evaporator freeze-up and cycle the compressor??

My All-Data clearly shows a temperature probe sensor mounted in the evaporator face- that is used to avert freeze-up- it may be bad- again a Tech II scan tool will decide..

the sensor you speak of is called the pressure transducer- it monitors continuously the high side pressure to turn on cooling fan(s) to disable a/c compressor if too low pressure- or too high

[Tech II]

Ah, the old semantic's pissing contest!

Haven't seen a wiring diagram call it a pressure transducer...

But you are correct, there is a temp sensor on the evaporator.......

If the sensor reading is too low, yes the control head will disable the A/C request signal to the PCM, to prevent a freeze up(which is usually accompanied by low air flow).....

Key to this is to see if the compressor is still running when the temp goes up(if the compressor stops, it could be the temp sensor...if it keeps running, more likely low on freon)......a scan tool would be needed, along with gauges, to compare the actual pressure in the system, compared to the data from the pressure sensor, and also compared to the temp of the sensor on the evaporator....with the system shut down, and pressures equalized, all three should be equal(transpose the temp data to pressure to compare to the gauge and to the pressure sensor).....then start the vehicle, and compare all three again to check the function of the temp sensor and the pressure sensor to the gauge reading....

In twenty years, I have never had to replace a temp sensor for this problem.....I have rarely had to replace the thermal expansion valve......more often than not, the problem is borderline refrigerant in the system, which depending on load on the system(humidity and outside temp), can cause fluctuating output temps.....

[trannyman52]

My 07 just quit display states a/c compressor shut off to protect engine.... 80 psi on system,,,compressor is not froze up ...where do you go from here????
going to run a scanner on it tonight...