The low pressure switch is made. It ties into the pcm, and the pcm fires the compressor clutch relay by supplying a ground to one side of the coil. If I jump out the relay, the compressor will run and cool. The pcm isn't firing the relay coil. Can't figure out why its not letting it fire. That's why I think it is TPI related. When you go to full throttle, the pcm cuts out the ac to give the engine all the power it needs to accelerate.

 

Sounds like you have it under control, however my next simple try would be swapping the relay, you could have a sticky relay situation.

 

Thanks Hongstertruck, Would you recommend an electric fan in front of the condenser? It should have it's own thermostatic switch maybe? ANy suggestions appreciated.

 

I have changed the relay, looking for wiring issues, and I am changing the emtc, I can get one at a parts recycler for $35.00.

 

Ok, here I am. I have changed the ETMC, the power computer, the high pressure transducer, the low pressure switch, the clutch relay, and have checked fuses and relays. I have checked wiring and connections between the pressure switch and computer, the transducer and computer, and the clutch relay, the clutch and computer. What other inputs control the ac?

 

A couple months ago, my neighbor went through and intermittent issue where his daughter's AC would work, then not work, then work, etc..., we traced wires for continuity issues, changed out the dryer bottle, changed out the pressure switch, compressor and the condenser, no fixes. Turned out to be the ambient air temp sensor on the front grill area. Now granted, it was a Jeep Patriot but, it seems like you are having pretty close to the same issue, might be worth it to try that part.
As far as another post about changing the fan to an electric one, a couple months ago, I changed my 04 F150 to a Windstar fan with a hayden controller and 2 relays, AC has been great since. I did a write up with full pics and instructions. Cost me around $100 total because I got the fan from a salvage yard.
Good luck.
Tom

 

I am in thee process of installing a pair of electric fans and a painless controller. Also I am using the compressor request signal from the emtc to operate a relay, and controlling the ac with a relay. I will add a hp control where the transducer is for a hp safety, and the compressor will cycle from the lp. I cannot see any reason this will not work. If it wont, I will add a toggle switch on the dash.

 

Please let us know if you solved your problem and how did you do it. I have the exact same issue and mechanic couldn't find a solution, said that it might be my PCM that is bad

 

I did a pcm, no help. If what I am doing works, I will post it here.

 

You replaced the computer and that didn't do it? Wow, how complicated can be to make a stupid AC work man, we've tried everything, when I bypassed the relay the compressor kicked in sonI know the compressor is working. I even changed the switch inside the truck just to make sure that wasn't the issue