1998 F150 XLT 4x4 4.6L Auto.

Bought this truck two months ago, the lot had the engine rebuilt due to bad bearings, so fresh motor. They forgot to recharge the AC, so I had them charge it when I purchased it. It blew icy cold every things until a few weeks ago. It wouldn't work, then randomly it would, then it would quit, etc. Today it's 97 and I had it on with my kids in the truck, hot air.

I tried turning it off and on, still hot.

I tried seeing if the temperature was stuck and moved it to hot, it got sweltering hot, back to cold, just warm air. There is no difference between vent and max AC.

I went to the store, picked up a refrigerant filler with gauge and a can of R-134. I hooked it to the low end of the system and was surprised that my pressure was about 60PSI. Great, they over filled it at the dealership. I released the pressure down to 40psi and checked, sill hot. I figured maybe something was weird and they might have mixed good refrigerant with bad and that's why it was intermittent.

I released all the pressure down to 0 PSI. I then put on the can of R-134 and filled it to spec. Sill hot air. I removed the harness from the pressure switch and jumped it, getting sparks when I connect the wire, so it's connecting, but still hot air, probably not the switch.

What's going on here? Could they have over filled it and killed the system or something? What is likely broken here? My heater works like a champ, my AC just blows environment temperature air.

 

Update: I pulled the shim from the clutch and now I get it engaging for a few seconds and then turning off. I hooked up the gauge to the low side and it goes up to 40psi when it's running and then drops back to 15psi when it kicks off. Does it just need more refrigerant? Was it just the shim on the clutch why it worked every now and then and the refrigerant was fine, but now it's low?

 

Update: Solved

After pulling that shim and getting the compressor clutch engaging, I put two cans of R134A in it until I hit 35 PSI.
What's cooler than being cool? ICE COLD!

 

your first thought should have been to look at the clutch and see if the compressor was running or not. If not running, and you have 60 psi on the low side, then clutch / electrical would be the first thought.. If you have power, then clutch is not engaging. LOW switch will drop clutch off about 25 psi........ above that ( 30- 35 psi) it should be running.

 

It was my first time having to work on the AC in any vehicle. I've had great luck and they've all just worked forever. I searched and then got to the few and started running through trouble shooting there. I'm just glad I went from hot air to cold air in a few hours, even if I did spend an unnecessary $35 on it.

 

If only you'd read the HVAC FAQs first....

 

Lol yup. Looked in the 1997-2003 forum, then the modular engine forum, after all that I found the hvac forum and fixed it, followed by a facepalm.