The radiator fan is supposed to kick on automatically when the AC is turned on regardless of engine temp. Mine is not turning on and I've blown up two compressors because of this. I think the relay in the picture is the culprit but I thought I would check in with the experts to figure it out for sure.

Mounted to the evaporator box on the passenger side.

 

 

Yes, but is this the AC fan relay?

 

That's the interior blower motor relay. Not the cause of the symptom at hand. I think the one in question is the same part #, just, that's not the one.

Meanwhile, if the fan EVER comes on, then the relay IS NOT the problem. If it comes on under certain conditions but not others, then the control circuitry is at issue, not the relay itself.

 

That's concerning. The fan does come on when the block gets hot enough but it does not turn on when the AC is on. It has to be a relay or fuse somewhere right?

 

Based on the description that you have provided of the Electric Engine Cooling Fan operation...

The most likely issue would be with the Air-Conditioning System Request Switch (can be a Pressure Cycling Switch, or High Pressure Switch) for the Electric Engine Cooling Fan.

I do not remember for sure...
However, I believe that 1989 TPI Cars used both a Pressure Cycling Switch and a High Pressure Switch for the HVAC System.
The High Pressure Switch, would then be responsible to act as Air-Conditioning System Request Switch for the Electric Engine Cooling Fan...
And NOT the Pressure Cycling Switch.

The Air-Conditioning System Request Switch is an Input of the PCM.
The PCM then uses an Output to Ground the Relay-Coil for the Electric Engine Cooling Fan.

I do NOT recommend "Throwing Parts at a problem".
However, I do not have a way for you to perform Diagnostics...
And the part is quite inexpensive.
Somewhere between $10 to $20.

Good Luck!

 

That's good info! My car is a TBI.
You said:
"The Air-Conditioning System Request Switch is an Input of the PCM.
The PCM then uses an Output to Ground the Relay-Coil for the Electric Engine Cooling Fan."

The PCM is controlling the fan because it runs when the temperature is high enough. It is not however sending a signal to run the fan for the AC which tells me nothing is telling the PCM it to send it. The only pressure switches in my AC (that I am aware of) are the low pressure switch for the Compressor clutch and the high pressure cut off on the compressor itself.

What diagnostics can I perform?

 

I am not going to type up all of the Diag Info.
Sorry.

The High Pressure Switch should be at the AC Refrigerant Compressor.
Usually a Dark-Green Wire will go from this Switch to the PCM.


The other Switch at the AC Accumulator, is the Pressure Cycling Switch.

 

So the PCM gets it's signal to start the fan from the high pressure switch on the compressor? I thought that was just to shut down the compressor if the pressure becomes too high?

 

On the TBI f-bodys the ECM has nothing to do with engine cooling fan. It is controlled by the head temperature switch in the passenger side head (along with...).

Along with the HVAC control head in the center of the dash. When the control is placed in a position that requests A/C (Max/Norm), this also grounds the wire to the cooling fan relay coil.

The head temperature switch and the A/C fan request switches are in parallel. So either one can run the cooling fan.

RBob.

 

Finally! Thank you! The control head activates the AC but no signal (apparently) is going to the fan. Is the HVAC selector switch (heat, ac, vent) that's broken?

 

I can't see what is bad from here. It may be the switch lost it's ground. Remember, this switch and the head switch provide a ground to the relay coil. The relay contacts are what carries the cooling fan motor load.

For testing can do a key-on, engine-off. Then ground the head temperature switch harness connector. That should activate the relay and turn on the fan.

Can do the same for the control head switch. Grounding the correct wire should also do the same.

RBob.

 

I'll give it a shot, thank you!

 

There should be a grey wire for the AC fan, cut it and ground it out and both fans should come on right away. On my 91 that's what happened anyway, I believe it was an AC pressure switch

 

Where did you find the wire? Was it in the interior or engine bay? I believe my problem is the HVAC control head not sending the ground to the fan control relay. I have to trace that out but I haven't tried to figure it out yet, kid is getting married this weekend and I've been busy as hell.

 

If you've got dual fans that wire should be on your secondary relay. The primary relay will have a dark green white stripe wire. Relays in the pics are primary on the left and secondary on the right

 

I just have the single fan. I'll figure it out, thanks!

 

It'll be one of those wires. Pretty sure

 

The OP is running TBI, is a single fan set up that has nothing to do with the ECM. You have a TPI set up that is completely different. You are leading him astray.

RBob.

 

RBob, I did the key on engine off test and found the culprit. On the electrical connector for the AC/Heat/Vent switch the last two contacts on the right are the ground and the wire going to the fan relay. The ground connector had partially pushed out of the connector so it couldn't make contact with the switch. I really appreciate your help, I could not have fixed this without it. And thanks to everyone else who weighed in, I learned a lot about these AC's.

 

Oh yea well when that info isn't mentioned in the OP makes it difficult. I'm also not a mind reader. So calm down. Stating the correct info right off the get go is best