Baffling A/C clutch issue

coopdog123

greased lightning
Clutch will engage when hooked directly to 12v source, i.e. A battery charger, but will not come on when plugged up to the truck harness. Getting 12v at the plug with A/C turned on at the dash though. Very confused.
 
I tried bending the male pins on the compressor side so as to provide a more positive contact with the plug to no avail. My amp meter leads were able to make easy contact woth the plug as well, no corrosion issues.
 
So when you probe both wires on the the connector (BK/Y & B on a '93) you get 12v with AC on, but when you plug the connector in, the clutch doesn't engage?

Reason I ask is if you're only probing the +12v wire and the other probe is grounded to case or bracket, then you may have a bad ground wire going to the connector. I've done this before and stumped myself!

If you're probing both wires on the connector, other possibility is there's a loose wire/connection inside the connector that's not making contact when the connector is plugged in, but when you stick that big fat probe into the connector slot it makes the connection. Had this happen before too - connectors do wear out and are easy to replace.
 
Correct^^ im probing both wires, not grounding somewhere else.

Im goint to use a couple paper clips and shove them into the plug to rule out your theory. I though bending the pins on the compressor would have ruled this out but they are very small so who knows
 
The big problem with a test light or multimeter is that they don't load the circuit. Just because you have voltage doesn't mean you have power. Try connecting an old school headlight to the connection with jumper wires. If it will light a headlight, both sides of the circuit are good. If it won't, connect the light to one side of the connector at a time using another source for power or ground as appropriate to see which side is no good.
 
Good point - especially for something like the AC clutch field coil, which does draw some current - it has a dedicated 15 amp fuse, not shared with anything else.
 
So i need to put what, at least 10 amps on it? If the voltage drops considerably with a load on the connector, what would solve the issue?
 
10A is plenty. Most circuits are designed to use a fuse that's double the expected current draw of the circuit. What you'll have to do depends on what side of the circuit you find the problem on.
 
You should be testing voltage WHILE the clutch is connected normally AND turned on. If you've been checking with it unplugged, that's why you're reading 12V - no load. Use the clutch as the load (of course).
 
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