91 F150 AC problem
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Junior User
Joined: Mar 2006
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91 F150 AC problem
Okay, since I know next to nothing about automotive ac I figured I would toss it out here and see what yall can come up with. I have a 1991 F150xlt, 5.0, E4OD, 2wd, reg cab. When I first turn on the AC after just a minute or 2 it blows ice cold. Then the compressor kicks out and the air out of the ducts warms up again, and the compressor doesn't kick back on. I just bought the truck about a month ago and didn't really mess with the AC when it was cold. By the way, the guy I bought it from said it was converted to 134A, and there is a sticker under the hood that confirms this, but I don't know what they actually did....please help, I'll die this summer without AC...
Fleet Mechanic
Joined: Feb 2006
Posts: 1,776
Likes: 5
From: Lorain County, Ohio
If the outlet temp is good for a minute or 2 then the compressor turns off the refrigerant charge is fine. 2 common failure items are the Low Side Pressure Switch on the accumulator. They often get fllaky like this. The other possible problem is an intermittant clutch coil. Works fine "cold" but when it warms up the coil opens.
When the compressor disengages, unplug the connector from the pressure switch and jumper it with a piece of wire. If the compresor starts, the switch is bad (~$10). If the compressor doesn't start check for power and ground to the clutch coil connector. If you have both, the clutch coil is bad (~$100 for the clutch kit). If you are missing power or ground, you'll have to dig a little deeper. It's possible that the AC relay is flaky, but this doesn't happen often.
When the compressor disengages, unplug the connector from the pressure switch and jumper it with a piece of wire. If the compresor starts, the switch is bad (~$10). If the compressor doesn't start check for power and ground to the clutch coil connector. If you have both, the clutch coil is bad (~$100 for the clutch kit). If you are missing power or ground, you'll have to dig a little deeper. It's possible that the AC relay is flaky, but this doesn't happen often.
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