1979-1993 & 94 Conv [Subscribe to Daily Digest] |
If both fans are coming on, it's not the low pressure switch. Even if only one fan comes on, it's not the low pressure switch. But if both fans come on and the compressor does not engage, it can't be the frost switch or ECU either, as long as the car is wired as-stock. If both fans respond to the A/C switch, the problem must be in the compressor supply. So what does that contain?
In a '91 U.S. market car, the compressor supply goes from the A/C relay through the the coolant overheat switch in the upper radiator hose to the compressor. The wire is red the whole way. Do you get battery voltage at the compressor? If not, jumper the coolant switch and try it out. Could also be your relay, especially if it's melted in the panel as you might be the case in your other post. That's a two-gang relay so it could conceivably work for the fan and not for the compressor, and the compressor draws a decent current so it could conceivably be melted, although I would think it would blow the fuse before it melted a relay. On the other hand, the relay's connection could be suspect especially if it's not coming out.
If you're already getting battery voltage at the compressor, then it's got to be a bad compressor clutch solenoid, compressor overheat switch, or fault therein. The compressor overheat switch is between the clutch and ground, if I recall correctly. It's a thing screwed into the compressor with wires coming out the side. If the compressor overheats, it will break the circuit. You can test this and it should have continuity through it. The solenoid clutch should also have continuity, although it might be a couple ohms. It can be changed out for a junkyard unit without taking the A/C apart. You might be able to sneak it out without taking the compressor off at all. Practice on a junkyard car. They say you need a puller to get the clutch off but I've always done them with my bare hands.
N.B. There is a fat diode in the compressor supply wire, forking off to ground. This may seem weird. It is supposed to be there. It is a snubber to ground the voltage spike from the compressor coil when you turn it off (typical of large inductors) so it doesn't mess with the radio, APC, and fuel injection components.
posted by 75.69.61...
, Wed, 30 May 2018 20:03:41
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