NO AC...Please help.

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Joined
Dec 13, 2008
Threads
163
Messages
3,549
Location
N. West CT.
Hello. Well its going to be hot soon and I still cannot figure out why my ac will not work. I cannot get power to compressor. Here is what I have done to troubleshoot and what I have found:

-Had AC charged at my local shop with vac applied.
-Went through FSM for checking AC amplifier harness with it unplugged and all reading where spot on
-I havent checked actual AC/heat control per fsm or rear heater switch. The hot to cold selection does work.
-The ac indicator does not light up when I put on defrost
-bought another AC amplifier (no dice)
-bypassed high low press switch
-power at AC fuse is good and has power to both sides of fuse
-ac thermistor checks out good at 1.2 ohm at 65 degrees F
-Only wierd reading I am getting is I get power going to ac thermistor of 5.3 v and sometime 1.3v. As per EWD these should be ground
-If I put 12v to the white/blue tracer at the ac amplifier which goes to compressor the ac works great. nice and cold. I think this would say that all ok with that part of the circuit which includes Engine Coolant temp. relay, ac magnetic clutch and temp switch

I have put quite a bit of time into troubleshooting and I have to say this is a pretty complex circuit for just ac compared to others I have worked on. I dont feel like paying a shop to diagnose but I am getting close to that point. I am giving myself and you fellow mud members (I thank in advance) to the end of the week and off it goes. Thanks Scott


 
Get a manifold gauge for pressure readings and report back.

Why was it recently charged?

Freon/134 doesn't get used up. If it was low then there is a leak. What was done to address the leak?
 
Cant do that. I dont have a gauge. The readings where in spec at a trusted mechanics shop. Either way the pressure switch is bypassed and the compressor would trun on regardless of pressures....correct?. Both of the seal for the condensor where leaking and have been fixed.
 
Autozone and a few other places will loan/rent out manifold gauges. And vacuum pumps.

Learning how to use them and more about my AC system was really worthwhile.

Edit: if you bypass the pressure switch and have power the compressor should turn if it's functional. Not sure, but is there a second pressure switch? Anyone with a better memory?
 
I am almost positive with the high low pressure switch bypassed that the compressor will turn on regardless of press. or vacuum. I am more leaning towards this being an electrical issue.
 
Apply 12v directly to the compressor to see if it still works.
 
still works off 12v direct to comp. and at white with blue tracer off ac amplifier
 
Double check your bypass on the pressure switch. I had a similar problem and the bypass was not making contact. I ended up cutting the wires, soldering them together and then heat shrinking them. I haven't been too worried about the compressor. I got a life-time warranty with it about 6 or 7 years ago.
 
Def checked that with a test light. power at both sides
Double check your bypass on the pressure switch. I had a similar problem and the bypass was not making contact. I ended up cutting the wires, soldering them together and then heat shrinking them. I haven't been too worried about the compressor. I got a life-time warranty with it about 6 or 7 years ago.
 
Ok so here is my update. I recently took the power from the green /yellow tracer which gets power from ac switch and spliced it direct to the white/blue tracer that feeds the compressor part of the circuit. Has been like this for the last few days and works GREAT! I just dont like fixing things the wrong way and still trying to find the solution the right way. I have gone threw the FSM with the EWD and everything checks out perfect except one strange reading.

As per fsm the check on pg 117 is for the ac ampl. plug. All the reading are perfect with the truck not running but with key on as per fsm. The reading between 8 & 9 which should be continuity is perfect with truck off with key on BUT when I start the truck and take that reading it shows +voltage of about 5v and sometimes 1.37v!!!!!!! It is actually feeding that voltage to the ac thermistor. Even if I unplug this connection it still wont work because I think the ac amplifier wont turn on the circuit due to this reading. Can someone please help.
 
Last edited:
bump.
 
Does it work if you rev. the engine?
There should be a little pot for idle threshold adjustment so the compressor will only come on after the certain rpm is reached.
 
ended up being a bad wire from dual pressure switch to ac amplifier. Not sending enough power but yet a little. I ran a new wire and it fires up now. Glad its in the past.
 

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