docmirror

I've tried the basics, and easy stuff. Could use some guidance. I can't get to my prints right now to look at the circuit.

Symptom: Key off, fans off. Key on, fans on high. AC button in, lights up - fans stay on. AC button out, light off - fans stay on. Battery fully charged, on a trickle charger. Car runs fine.

Diagnosis:
1. Jumper top of intake sensor connector closed. Leave wires off sensor open.
2. Jumper front of fan lower sensor closed. Leave wires off sensor open.
3. Try all combos of two sensors open/closed, open/open, closed/closed, closed/open.
4. Swap fan amp on front deck.
5. Swap fan controller under pax seat side cover.
6. Remove fuse from 28 - one fan goes off.
7. Remove fuse from 29 - other fan goes off.

Every minute or so, the fans slow down just briefly, then speed back up. I presume the fan amp is working as it should and trying to clamp the current to the fans but failing. I think there is a timer circuit involved that keeps the fans on after key off based on one of the sensor switches. There is no fan relay(s) in the relay chart, unless they are located somewhere else. However, the failure mode doesn't sound like it is relay related, as both fans operate exactly the same. When I bought the car, the fuses were removed, and the fans didn't run. As soon as we put the fuses in, the problem appeared. So - clearly the OP experienced this, and just pulled the fuses as a 'fix'. sigh...

Ideas, thoughts, suggestions?

soontobered84

Doc,
Is the AC button activated on the dash? Maybe there is a short or some kind of creative wiring associated with that button.

docmirror

The AC button is in - the light is ON. AC button is out - the light is OFF. As I understand it, this is nominally correct operation of the AC circuit. I'm thinking of taking the connectors off the HVAC module next.

soontobered84

So there is no difference whether or not the button is in(activated) or not.

If there was creative wiring, I would think that pulling one of the fuses would kill both fans, so that is probably not a cause.

The AC does have a certain amount of control over the left fan, ie. the AC button turns on the demand for the fan, but I'm betting that the sensor on the bottom of the radiator is FUBAR and sending signal to the fan controller that the engine is too hot and needs the aditional fan cooling.
I believe I have an extra sensor floating around if you want to test it.

See you tomorrow.

Bigfoot928

Dead short somewhere

docmirror

The rad sensor has been bypassed with a jumper. The sensor is not sending any info to the controller. The jumper on the wire connector is either open, or closed. When I have the jumper in it is closed. When I remove the jumper from the connector it is open. All combos have been tested along with the sensor connector on top of the intake. It is not a sensor problem.

I removed all the connectors from the HVAC, including the connector to the AC button.

New symptom: The RIGHT fan runs on high with the key on, it does not run with the key off. The left fan does not run at all now. The right fan runs on high for ~30 seconds, it drops down to low mode for a few seconds, then changes and goes back to high operation and the cycle continues. This is true with every combination of the sensors. open/open/, open/closed, closed/open, closed/closed. The sensor connections make no difference in how it runs. I believe there is a fault with the HVAC circuit as well, but something else is also going on to keep the right fan cycling. It will not shut off when the key is on.

BTW, key is on, but engine not started. I don't think that makes a difference, but I'll run the engine and see if there is a change.

soontobered84

Is the manifold air temperature sensor functional? That's an "on and off" sensor, right?
I don't have an extra one of those.

Mark Anderson

Intake manifold temp sender shorted?

killav

Doc,

What year car? Auto or Manual?

There is a temp sensor in the auto trans that also can also cause issues.

soontobered84

Mike, It's an 88 AT.

docmirror

I have both connector wires off. The sensors are not plugged in. My presumption is that open is the default condition, but I have tested with the wires shorted for both sensors and no change. Right now, both are open at the sensor connector.

I'm going to try another fan amp. When it goes down for a few seconds, then back up, seems like a power amp failure, but not sure.

docmirror

...

Alan

Try removing & replacing the fan & flap controller (clean the connectors) - if no good try a new controller. This is under the cover next to the passenger seat.

The final stage drives the fans - the controller decides when to activate the fans - they are usually very reliable, I've not heard of one failing (but they must fail occasionally) - used still would be a good bet IMO.

Alan

docmirror

That has already been swapped with a known working unit. When it cools off, I"ll try the amp.

Mrmerlin

Doc try replacing the fan fuses make sure that each one of them fits tightly in the CE panel
if not add some solder to the fuse leg to thicken it, then push it in. Use Doxit 100
make sure the fan wires at the POSITIVE terminal are both clean and tight