Did all the basic check fuses/relays. ECT has been changed, relay swapped for known good one. Fan works if I remove relay and jumper 30 and 87. I'm down to where I did the 470 ohm resistor across the ECT connector contacts and still no fan. Any ideas? Oh yeah 94 cherokee I6.

 

Given that fan works when relay is bypassed, I would try another relay or check the relay socket and wiring real good.

I have had "good" relays that click indicating the primary side functions, but the contacts for the secondary side were failed.

 

I tried multiple relays and then I picked a new one, all with the same results. I also ran test leads from relay socket to the relay to perform the following. With the leads connected from the socket to the relay as if it were plugged in I get as expected nothing. If I then pull the lead out of 86 and connect it to ground the fan goes on. I appears the PCM is just not providing ground when at temp. I checked the ECT connector with my meter and I get 5 volts going to battery ground on one terminal and no volts on the other. I also get 5 volts going across the two terminals. I'm kinda stumped.

 

These are tough. Try cleaning cable connectors and grounds. I have even decabled/clean/recabled the ECU (Computer) just to get stuff to work right. Or at least eliminate a possible issue. And service all the grounds per Cruiser54 or CCKen's advice. Its all written up on the Forum. Mfgrs cut a lot of corners trying to use the car body as the load balancing path of the circuit. Only a good idea on the showroom floor. After a few decades of field service these connections degrade.

 

I completed A/C hookup and charge only to find out that aux fan will not come on with A/C either. If I jump 30 to 87 on A/C relay I get A/C but no fan. In diagram below I have checked and diagnosed fuses and relays in the dotted line PDC box below but do not know where to find supposed fuse at top of diagram connected to ST-RUN-A21. I don't have a single 20amp fuse under dash and nothing labeled accordingly. THIS FUSE WOULD EXPLAIN LOSING BOTH. Any help would be appreciated, Thnx

 

Ever disconnect coolant temp switch yet ? Try jumping ac pressure switch yet ? If fan comes on by doing these id suspect cts or not enough freon pressure to activate low pressure.

 

Did the coolant temp disconnect early on with no results. Ditto on the low pressure switch. I jumped 30 to 87 on A/C relay to force the compressor on so I could charge the system still no joy although pressures and good cold air proves A/C works. None of the above will get the aux fan to come on unless I jump 30 to 87 on aux relay. Both ECT and low pressure switch are new. Swapped each relay with known working and still no joy. This A/C system worked before I tore everything apart for rebuild. Ugh.

 

Check grounds at relay socket gotta have both or no worke... Check ground wires at dip stick and fenderwell by battery.

 

Never thought to read codes as I didn't have a CEL and i knew the bulb worked. Having run out of ideas I figured what the hell. Well I have codes!

Open or short AUX Fan relay circuit
Open or short A/C clutch relay circuit
ECT voltage max or min exceeded

Now that's a fine Howdy Do. Clearly my engine harness is FUBAR.
I'm envisioning it spread apart on my garage floor.

As a start I think I'll clear the PCM and leave the ECT disconnected as I just replaced it and see what codes come back then plan for a long weekend.