Cooling mystery

tchort · 11-06-07, 12:34 PM

Hi everyone, I just came across your forums while researching this problem that's been making me lose sleep for the past several months. I think if there's any hope of me stumbling across the solution, it's sure to be here.

I am the proud owner of a '88 Z51 4+3 that my girlfriend appropriately refers to as The Batmobile. I also invested in a GM shop manual for the car (more on this later).

Here's the problem: The auxiliary fan refuses to turn on. The fan itself works. I give it 12 volts and it comes on fine. But, it does not come on when I turn on the AC. Also, it no longer turns on in Diagnostic Mode when I jumper A and B on the connector under the dash. Instead, what I get in Diag Mode is a fast clicking sound coming from somewhere near the top of the engine, under the TPI.

I know this is probably caused by low freon in the AC system. But what is confusing is that the fan no longer comes on in Diagnostic Mode either.

I sure would appreciate any help with this. The GM manual is complete garbage (with all due respect). It makes NO mention of a fan switch on the left side of the engine that controls the main fan.

Thanks in advance.

Hrtbeat1 · 11-06-07, 02:13 PM

Most likely a bad relay. Could be the clicking that you hear. There should be two relays one for each fan.

G

tchort · 11-06-07, 02:17 PM

Thanks for the reply, Hrtbeat1! Do you (or anyone else) know where the auxiliary fan relay is?

Hrtbeat1 · 11-06-07, 03:49 PM

Not exactally sure for an '88. For My '90 its one of the two relays on the side of the radiator shroud, on the drivers side.

G

gmjunkie · 11-06-07, 04:11 PM

Quote:

Originally Posted by Hrtbeat1

Not exactally sure for an '88. For My '90 its one of the two relays on the side of the radiator shroud, on the drivers side.

G

Yep!!Thats where there at!!

tchort · 11-06-07, 04:22 PM

Ahh, you're right. Makes sense; that's where the main fan relay is. The only thing is both of those relays have been replaced already. That's one of the things my mechanic tried before giving up. ;-)

Assuming the replacement relay is good (I've yet to check it) what else could be the problem? Is there a fan switch built into the AC system that could have failed? Or is there something else going on here?

gmjunkie · 11-06-07, 04:40 PM

Quote:

Originally Posted by tchort

Ahh, you're right. Makes sense; that's where the main fan relay is. The only thing is both of those relays have been replaced already. That's one of the things my mechanic tried before giving up. ;-)

Assuming the replacement relay is good (I've yet to check it) what else could be the problem? Is there a fan switch built into the AC system that could have failed? Or is there something else going on here?

Bad ground can make them do funny things,and if I remember right that fan won't run untill it reaches 228 deg or unless the compresser is running!! If it's low on freon,the compresser is not running so it won't run!!

tchort · 11-06-07, 05:09 PM

Quote:

Originally Posted by gmjunkie

Bad ground can make them do funny things,and if I remember right that fan won't run untill it reaches 228 deg or unless the compresser is running!! If it's low on freon,the compresser is not running so it won't run!!

Right, but the auxiliary fan should run in Diagnostic Mode regardless of how much freon is in the system. And mine doesn't. Instead, I hear that clicking which is not coming from either of those relays on the fan shroud.

So either my AC is out of freon AND another "link" in the fan circuit is broken, OR there is something going on in the circuit that's preventing the fan from coming on in both situations - with AC running and in Diagnostic Mode.

Any thoughts? Anything wrong with my reasoning above?

tchort · 11-06-07, 05:13 PM

BTW, when coolant temps reach 228 the MAIN fan turns on (the one that's located at the very front of the car, visible under the front bumper). The auxiliary fan (the one that's visible with the hood open) is not linked to the temp switch that energizes the main fan circuit.

gmhowe · 11-06-07, 07:32 PM

Ok so the fan that is right in behind the radiator is the AUX fan ?? I thought the one that is front of the oil cooler ( the small fan ) was the AUX fan, sin that is the one that kicks on at 180' on my 85'

Gordon

tchort · 11-07-07, 11:00 AM

Gordon - is your fan running even when you're moving faster than something like 25-30 mph, or just when you're sitting still? By the book, those fans are not supposed to come on while you're in motion unless the AC head pressure reaches a certain psi or your temp goes past 228. (At least by the manual I have, which is for my '88)

Anyway, anybody have any thoughts/comments on the problem with the non-functioning fan in Diagnostic Mode?

Robertwav1 · 11-07-07, 01:47 PM

Quote:

Originally Posted by tchort

Gordon - is your fan running even when you're moving faster than something like 25-30 mph, or just when you're sitting still? By the book, those fans are not supposed to come on while you're in motion unless the AC head pressure reaches a certain psi or your temp goes past 228. (At least by the manual I have, which is for my '88)

Anyway, anybody have any thoughts/comments on the problem with the non-functioning fan in Diagnostic Mode?

Like Junk had said, a bad ground can make them act strange. That means in diagnostic mode also. My car has several grounds along the frame rail. Yours probably does also, I would clean these up. Inexpensive and probably needs to be done anyway.

tchort · 11-08-07, 12:21 PM

Quote:

Originally Posted by Robertwav1

Like Junk had said, a bad ground can make them act strange. That means in diagnostic mode also. My car has several grounds along the frame rail. Yours probably does also, I would clean these up. Inexpensive and probably needs to be done anyway.

Well, I was afraid of that!

Guess I'll have to bite the bullet and meticulously look over the wiring. What do you recommend I use to clean the connections? Do you then apply any dielectric grease or anything like that?

Robertwav1 · 11-08-07, 01:59 PM

Actually it's a faily easy to locate the grounds. Just start a the front of each frame rail and work your way down to the firewall from the topside of the car. You'll see the ground areas. I didn't put anything on mine, just cleaned them up. Maybe others will lean toward a grease or paint of some sort. Also under the car, around the bell housing I found 1 or 2 grounds that needed attention.

gmhowe · 11-09-07, 12:58 PM

Don't know if they are on while moving but the small fan comes on at 179 180 degrees and stays on while standing still. Still can't figure why the large fan in front of the engine only comes on at 228, seems a little late at that temp.