97 Dakota 4WD 318/auto

Where does the compressor clutch get its signal/power to engage?

I am thinking it from the computer through the low pressure switch then high pressure switch finally to the clutch. Is there a WOT relay on those? I have already swapped the power relay and tested for power back to the low pressure switch with no power (using a test light).

Can I jump the clutch and coil with straight power to test it? I am assuming the system is grounded and gets a power/positive signal to engage.

Thanks in advance, Kevin

Did you ohm out the low/high switches to make sure they are closed. Also if to low on refrigerant the comp will not kick In

I've heard rumors of a "WOT cut-off switch" but there is no physical switch. If any such switch or feature exists, it's all in the programming of the PCM, since the signal for the clutch ultimately originates from within the PCM.

Printed and saves.

Thanks

The PCM moniters the low and high press switches and the dash switch and when it sees that voltage go low it knows you want AC and then if all the switches are right it will then ground the AC clutch relay. Course the PCM uses the TPS signal to know when full throttle is asked for and will cut the comp at full throttle. Ron

Thank you, today's PCM swap (known good from one of my other trucks, actually the original from this truck that the cruise circuit felled on a year or so back, but the A/C circuit is fine) didn't cure it and I really didn't have time to diag it so it will wait til next week end.

So I finally got back to it and what I found was no power to the relay (it was there on my 99 wioth either computer), it gets the trigger when the A/C is turned on but no constant power to it. I don't see any fuse in the circuit and when I pulled the PDC I found no obvious burnt wires. So in an effort to further diag it I ran a power wire to it and it engaged and everything worked properly for about 2 moinutes then is melted my bypass wire which was fairly small gauge (on purpose). I then wired the relay outside the box with a fuse on the power wire, it worked fine until I engaged the clutch and then it popped the fuse. So to me the clutch is shorted or has high resistance anyway. I'll swap it out to test and see if everything else is OK. So I have 3 questions, first is there a fuse in the system I am overlooking, second where does the power to relay come from and finally is it a 12 volt feed.

yes,
there are 2 fuses.(before the relay, nothing after) If they are not labeled, use a test light and with ign on, check all fuses for power on both sides. if test lights only lights up on 1 side of the fuse, it is blown. typical relay uses 4 wires. 1 constant 12v power, 1 ignition 12v power, pcm controls ground circuit, output to the device.

Thank you, I didn't test the fuses cause they are all labeled for other devices and I haven't noticed anything else not working but it's cheap and easy to test them just to be sure. It is a 5 pin relay by the way but not sure what the fifth leg is, but I beleive you are correct on the 4, I was jsut making sure it wasn't a reduced constant power. I should have time to do some more testing tomorrow and will update.

Well I finally got back to it today and finished it. The clutch was shorted and that was blowing the fuse. I did finally locate the fuse with the test light, it was in the power distribution box cleverly labeled A/C Clutch, don't ask me how I missed it, I will just amuse I'm an idiot. Once I fixed that I removed my wiring harness I built to supply fused power out side the boxa dn returned it to the factory set up, works like a champ. Just thought I would close the thread.

Thanks for the help folks!