Automotive Air Conditioning Information Forum

The air conditioning on my 2011 Dodge Ram 1500 5.7L all of sudden stopped working, it worked great before this week. When I turn on the AC I hear something click for a split second but the compressor nor electric cooling fan click on (the AC indicator stays lit up on the dash). I checked the low pressure with gauges and I’m getting ~30 psi on the low side at 70 degrees ambient temperature (in spec). All of the fuses and relays tested fine. I am not getting any voltage to the compressor clutch. In my research I read that the computer cuts voltage, if the clutch coil pulls more than 3 amps (I didn’t see this in the service manual). I am tempted to feed the clutch 12 volts manually but I was afraid to back-feed the PCM.
Thanks in advance!
Joe

You can disconnect the hot lead to the clutch and feed it from the battery without frying the PCM. Put a fuse in the line for safety. First thing I would do is verify correct refrigerant level in the system. Is this a manual or automatic system? The fact that both the cooling fan and compressor does not get 12 volts is a clue to check the charge.

30 psi with the compressor having not started is not good. You have a leak-out. Static pressure at 70 F should be about 70 psi. The switch needs about 45 psi to be certain to close.

you have about 5% of needed refrigerant in your system--- find your leak..fcix it, evacuate and recharge to factory spec compressor will come on when you put in the right amount of refrigerant.

Thank you all for the replies, very helpful! I was thinking the low pressure cutoff was below 30 psi, since when the compressor is running it can be as low as 20 (based on the chart). I now realize the low pressure cutoff is used before startup.

Can I temporary bypass the low pressure cut off by running a jumper between terminals? Before proceeding I want to ensure the compressor will kick on.
thank you
Joe

Don't run the compressor without a full charge.

You know that the charge is gone, all of a sudden because something sprang a leak. Take care of that and it will work again.

Ok, got it. To refill the system after fixing the leak, doesn't the compressor have to run in order to suck the refrigerant in?

No.

The system mus be evacuated after repairs are completed.

The vacuum in the system will allow the refrigerant to be added.

Jumper wires sell lots of parts. Bypassing switches lets the compressor run without oil.

If your pressure verses ambient temp relation readings are correct then GM gave your answer for low charge

I had a friend stop by to take another look at the ac in my truck. At rest the low and high side were about 75 psi. The compressor and fans kicked on when the ac was turned on. However, this resulted in no change to the high and low pressure. The compressor sounds normal. Is the compressor shot or could it be a blockage? Thank you
Joe