aux fan trouble, relay maybe

95 xj, 4.0, aw4.

a couple weeks ago i swapped my 8 blade aux fan for a 10 blade unit from a 98 xj at the junk yard. i got looking under my hood tonight (pondering a taurus fan) and it dawned on me that i havent heard my aux fan come on for a while. so i unpugged my ac comp (ac doenst work right now), set the ac control to defrost and started her up. the aux fan did not come on.

initially i thought it might be the relay. so i pulled the relay and swapped in a new one. no go. it almost seemed like the female connection was loose at first. i could have the relay just barely resting on the female connectors in the pdc. when i jiggled the relay just right, the relay would click for maybe a second then stop. when the relay was clicking, the fan would turn on briefly.

thinking it was loose wires inside the pdc, i removed the relay and tried running a wire from each post on the relay (save for the unused center post) to the corresponding socket location. again, the same clicking for about a second and the same result for the fan. not a loose wire. replaced relay

i thought that maybe the new fan was too much load for the relay. i removed the load (unplugged fan and inserted the lead from my DDM into the connection). there was no volts at the fan connection. again i removed and placed the relay back into its socket with minimal pressure and jiggled it arround. i got the same clicking and was only able to tell via the ddm that it had juice for a brief period, but nothing that i could get a reading off of.

again i removed the relay. this time i jumped the terminals. from left to right and from top to botom. the fan turned on and ran strong. i know that its not good to run a fan without a relay. after verifying that the fan does infact work, i put the relay back in its place.

durring the above i swapped the fan relay for a known good starter relay and also two new relays from vauto zone (NAPA isnt open this late near me).

i searched for aux* fan and rummaged through 10 pages of results. i didnt quite find the information i was looking for.

any ideas? oh, and im in arizona, so going without the aux fan is not advisable. i would prefer to keep it controlled to automaticaly come on as i am a numbskull and dont stare at my temp guage constantly as i drive.

TIA
stewie

the a/c system has to build pressure for the fan to run when mines low on refrig. it wont run

kennzz05 said:

the a/c system has to build pressure for the fan to run when mines low on refrig. it wont run

Click to expand...

That's not with a '92 Cherokee. With the depresserized A/C my E fan is running.:wave1:

kennzz05 said:

the a/c system has to build pressure for the fan to run when mines low on refrig. it wont run

Click to expand...

ditto

from my understanding on the pre OBDII would come on regardless of ac system pressure. and i remember it coming on a couple of months ago. ac has been broke for two years.

Anyone?

I thought on the early models the AC clutch had to be plugged in to trigger the relay. IIRC (and there's no guaranty of that) the clutch is the ground for the control circuit on the fan relay when there isn't a temp related demand for the fan. Plug the AC in and hit the switch (AC) again for a quick test (if your AC isn't working just look for the fan to move and shut off again)

My a/c doesn't work at all, but the new aux fan does come on when engine temps. warrant (220ish). Not to hijack, but is there a visual check to see if the a/c compressor works? I just know that the expected a/c noise and power drain/engine load does not show up when I turn it on. That and it only blows hot air.

kujito said:

My a/c doesn't work at all, but the new aux fan does come on when engine temps. warrant (220ish). Not to hijack, but is there a visual check to see if the a/c compressor works? I just know that the expected a/c noise and power drain/engine load does not show up when I turn it on. That and it only blows hot air.

Click to expand...

the front of the compressor would be turn ing if comp is running

for the benifit of anyone searching, the "problem" is resolved. I run the engine today with some newspaper placed against the grill to aid in speeding up the warm up process. (dont cover the whole grill). when it got hot enough, the fan kicked on. i guess it must be wired so that it does not turn on with the ac when the ac system is inop.

Another way to test if the e-fan circuit works is to disco the cts(at the t-stat housing). The ecu will kick it on as a safety measure(better to overcool w/o a temp input than to overheat).

Shorty said:

I thought on the early models the AC clutch had to be plugged in to trigger the relay. IIRC (and there's no guaranty of that) the clutch is the ground for the control circuit on the fan relay when there isn't a temp related demand for the fan. Plug the AC in and hit the switch (AC) again for a quick test (if your AC isn't working just look for the fan to move and shut off again)

Click to expand...

My 87 E-fan runs without the A/C compressor plugged in. In fact it runs continously since it takes a/c pressure to turn it OFF. As soon as you move the control to a non A/C (or defrost) position it turns off.

I currently am using the A/C mode as cheap way to activate the thing since my fan clutch is dying.....