No AC. Where to start?

[Purefection]

So my truck hasn't had AC since I bought it. Previous owner says it worked.

So far I have: changed the AC relay. Checked fuses. Changed the climate controls in the dash(although these were from a wrecker so I'm not sure if they are good. The heat works fine). I've recharged the system and it was fine and had no leaks.

When I press the AC button, nothing happens. The compressor doesn't even audibly kick in.

Also, maybe unrelated, but my position control doesn't work either (stuck on defrost). If I put it on face level it comes out a bit but mostly full defrost.

Just wondering where to start self diagnosing my AC system. This summers been a hot one!

 

[badazzbulldog]

try another dash control if you can they tend to burn up inside

 

[east302]

You might also check the low pressure switch on the side of the accumulator. It will kill power to the compressor. Unplug it and jumper the wires in the harness. If the compressor kicks on (make sure it's turned on on the dash control) it's either a bad switch or low on refrigerant.

The switch is maybe $15. I think that it's also called a clutch cycling switch or something like that.

 

[Fredridge]

if you have the digital display it may be a common problem, you can do a search on here and find it... I had to pull the wiring harness and pull pin one out of the harness, mine works great now

 

[Purefection]

Not the digital display. Will check the low pressure switch. Refrigerant is full and at proper pressure according to the guage I have.

 

[Incredible Hulk]

Do you have power to the compressor clutch?

 

[96Z71ECSB]

If the compressor is not running when you checked pressures, then the pressures are incorrect.
The AC system needs to work properly in order to read the correct pressures (both high and low pressures).
The low side pressure should read anywhere from 60psi to 100psi with the AC system turned off. If the pressure reads lower, then there is not enough freon in the system.

If the AC system is working properly, the low side pressure should read anywhere from 25psi to 40psi depending on the ambient temp outside.
If your AC system pressures are 25psi to 40psi with the AC compressor not working, then add a can of freon. I would bet that it with kick on and start working.

Good luck!

 

[Purefection]

Last time I tried to add a can it would physically not go in. Is it possible it's over full and causing it to not work at all? When I turn the AC on in the cab the compressor doesn't kick in. Hasn't since I bought it

 

[Scrufdog]

Try jumping the switch on the accumulator and see if the compressor runs.

 

[96Z71ECSB]

I found this: http://www.silveradosierra.com/how-...k-series-trucks-hvac-control-unit-t77522.html

I don't know what year your truck is so I hope the article applies.
Scroll down to about half way and he has a picture showing the locations of all the AC system switches. He also explains how to check each switch.
Beware that each switch is connected to the ECU, so if you try to jumper any of the switches with 12V power, make sure you have the right wire.

The whole article is actually very interesting.

Good luck!