I have a 97' 2500 12 valve. The a/c compressor wont kick on and no matter where i put the dial it wont change from defrost. i have filled it until it is in the red warning area and it still wont do anything. I know it isnt the freon level. Ive heard about this a/c clutch relay so i will check that but many others said that didnt fix their problem. Can anyone help??? It is way to hot to be driving without a/c right now!!!!!

 

If the A/C compressor is running and the cab is still hot then check your damper door in the heater housing. They frequently stick and allow hot air to keep right on filling the cab.

A vacuum leak in the A/C control assembly, or elsewhere in the vacuum system will also keep the A/C from switching on.

The other frequent failure point is what is known as a fixed orifice tube. It can be easily replaced but requires system evacuation to do so.

 

Big Red, first things first, make doggone sure your harness is plugged into your compressor, then on your drier, there is a low pressure switch, take the connector off and jumper between the plugs to make the circuit. Check to see if that kicks on the Clutch ( engine running, max AC of course ). If it doesn't, then it is time to check the relay and perhaps apply 12V directly to assure the clutch isn't burnt.

BTW, it is never good to overcharge systems, if it doesn't cool with the correct pressures, you have other issues.

 

I second patdaly on the electrical stuff. On the vacuum, you should trace the line from the vacuum pump to the firewall first, and make sure you have vaccum at the firewall connector. Been there, found some kind of restriction in the vacuum line, after the exhaust manifold burned a hole in it (oops) and I had NO vacuum getting inside the cab.
If you find that you cannot get the air to come out of the dash vents, it will be the actuator just above your right foot under the dash. There's a TSB on this problem, that oil can get through the vacuum line to this actuator and the oil eats the rubber diaphram in the actuator causing it to stop working. Been there, replaced that, on my 96. Of course, I had other vent settings, just no dash vents.

Chris

 

For AC you need to get some gauges on it and see what the readings are, also check all connectors to see if they are for sure connected (i.e. disconnect and reconnect just to make sure).

For the vent not blowing anything but defrost, you need to check all your vacuum lines. The vent settings are vacuum on these trucks and default is defrost when it doesnt get vacuum to it (this is a safty, that way you can always clear your windshield).

 

If you added freon(into the red zone) without the compressor running, you probably have overfilled the system. I would release enough freon to put it back to where you started, then troubleshoot why it isn't cycling. Worry about the freon after you get it cycling.

 

The only reason i over filled the system ois because severalpeople have told me that my pressure switch might be sticking and that the overage of pressure might mae it kick in. I willd definetely look into the vaccum lines and see if I can solve that problem. Thanks for all the input. i will post again when i get it resolved!

 

If you are putting freon in the system without the compressor on, the pressure should be in the red. The pressure on a system without the compressor on should be about 65~75 psi (both high and low side). Once the compressor kicks on the pressure on the low side should be 20~25 psi.