Automotive Air Conditioning Information Forum

Have 07 Uplander that blows the air conditioner fuse after about 10 minutes. I watch with an ammeter is the current went from about 8 amps to 12 amps over 10 min. Slowly climbing. I replace the AC coil and the unit and the fuse last much longer but still with the same results of a blown fuse. Even if there was something wrong in the AC system like an overcharged I don't understand how it blows this fuse. They are to separate systems

Be sure all your electrical connections and connectors are very clean and shiney, and that the compressor is grounded well, unless the coil has its own separate ground wire, in which case be sure that is clean and that you actually have a good ground.
Poor connections will heat up and draw more amps.
Are you sure you are using the correct fuse rating?

You can also put your fingers on all the connectors and check for any that are hot or warm, they are the bad ones

Thanks for the reply, but I have to disagree, dirty connector means less current as the voltage will drop across the connector. If coil has the same inductance, with less voltage, that's less power

Have it your way

An additional thought: Is there a diode installed in the wiring harness near the connector that plugs into the compressor?

In general the coil current (and the magnetic field) drops as the coil heats up.

The only time a coil draws more current when hot is when it expands physically and begins to short turns - connection the windings in parallel and raising the current.

But you say you have replaced the clutch coil. And that it is doing the same thing again. Not a common failure, and a second time would be pretty rare.

To rule out the replacement coil disconnect it from the system at the compressor when cold and measure the coil resistance. Then run the system for a few minutes, and re-test the coil. If the resistance does not increase from cold to hot the coil is defective.

It is important to test at the coil, so that you are only testing this component.

If you determine the coil behaves normally, repeat the hot and cold resistance testing at the relay output terminal on the clutch relay socket. Check from the relay output to ground for resistance with the relay removed.

Clutch coil should only be pulling 3 or 4 Amps, was the harness leading to the clutch repaired? Is the harness meliting down every time you try it? John is probably right, diode in backwards in the harness or the plug, diodes can also be internal to the clutch coil, molded in, and you might have a fabricobbled together harness that is backwards.

I pretty much would be concerned with other issues causing the repeated clutch failure. Does the body of the compressor feel hot after running for a few minutes?

Thank you for all the responses. We'll have to do some additional testing. I'm going to put 12 volts to coil I took out and see what the results are. I'm also going to watch the current in the current coil as it goes up turn the car off and then turn it back on to see if it time-critical. I also have to do some reading on back EMF that magnetic field to see if possibly the voltage at the coil is going up,

Tested the coil, cold it is 2 ohms, current starts at 6.5 amp and rises. Coil gets to hot to touch, current at 10.5 amp, resistance is 1.4 ohm. Using a 12 volt battery as a supply. Both coils do this, the new one and the old one. If I run at 8 volts everything stays stable, So now, does the coil require 12 volts or something lower?
Both coils defective? the same way?