rfcomp

I have done some reading on this issue but keep seeing conflicting information. I have a 1990 RS with the 5L engine with a single fan. At the end of last season I got the A/C re-installed and working then I put it away for the winter. My rad fan worked as it was supposed to before the A/C work was done. I am pulling it out of the garage for the season ,now my fan is on all the time even when the A/C is off.I have heard that with a single fan setup you do not need to attached the connector to the A/C high side fan switch . If I disconnect this my fan does not come on at all even at the point of overheating. As soon as I reconnect it comes on and stays on. I have tested the switch and it seems to be normally closed, I would think it should be normally open. I talked to the mechanic that did the A/C work and he said I must have the connector on that switch. Any idea's?? Thought I should mention that I am thinking of going with a dual fan setup at some point. Any help would be appreciated.

henryd3

iTrader: (128)

Is the slider on the HVAC control in the dash set to either AC or defrost?

rfcomp

No the sliders are off.

dmm3369

Maybe the fan relay is stuck. I had one of mine stay on and it was the relay on a dual fan setup. Worth checking.

henryd3

iTrader: (128)

I know, dumb question but had to ask??

rfcomp

There are no dumb questions, I'll definitely check the relay, thanks.

rfcomp

I checked the relay, it is good, as well a friend of mine has a Camaro, tried substituting his, fan on all the time when the AC high pressure switch is connected. When I disconnect the AC switch no fan at all.

deadbird

The single fan, for a 305 TBI engine is neither controlled by the ECM, nor the A/C high pressure switch.

It sounds like the fan relay may have possibly been rewired back in, incorrectly.

A TBI fan relay coil is controlled only by ground, via the fan switch in the block or, the HVAC control in any A/C position. The relay coil positive side is powered by an ignition switched power source.

henryd3

iTrader: (128)

It sounds like the relay and fan wiring is working great, but something in your HVAC control is acting like it's set to AC on. Not sure how that could be but possibly that is where the miscommunication starts??

rfcomp

With the AC fan switch disconnected I disconnected the wire to the switch in the block and grounded it, the fan came on right away so I figure either the switch in the block is bad or there is an issue with the HVAC controls. Thanks for the info I think I'm getting close.

deadbird

I apparently misread you stating 'high pressure switch' (on the compressor) as opposed to you actually stating, the a/c fan switch (on the hard line).

The fan switch is a redundant ground to the fan relay and should be open until it reaches 232psi line pressure, it then closes to ground.

All three are tied together... if one fails, the rest should still work.

henryd3

iTrader: (128)

This means your relay and fine are working just as they should, that's what it's supposed to do. It's the signal from your HVAC saying either you're set to AC or defrost on that is doing it. Don't have any idea how that is happening however, sorry
The fan switch wouldn't turn the fan on until the temps get way up there

rfcomp

That wiring diagram helped, I removed the AC pressure switch and found it to be stuck closed, or a normally closed one was installed, and I checked the fans switch in the block once the car started to overtemp and found the switch did not close (no continuity between the switch and ground) so looks like I have two issues I will replace both and hopefully everything works. Thanks for the help.

henryd3

iTrader: (128)

Those switches are famous for failing largely to their poor design. Lots of options though for switches that turn on at lower temps. Make sure you check those out.
Good luck with it