Welcome to the Corvette Forums at the Corvette Action Center!

Help! Fan doesn't come on with A/C on

chris123

Well-known member
Joined
Jul 7, 2006
Messages
75
Location
Wilkes Barre, PA
My mechanic just recharged the A/C on my 1986 (C60 manual), and when he turns the A/C on, the fan will not come on as it should. It functions properly in regards to the coolant temperature, on at 225* and off at (not sure of exact temperature); he said he grounded the wire on one of the pressure switches, (simulating the head pressure signal going back to the ECM), and the fan still won't come on when the A/C is on; the A/C will only stay on for a minute or so until the high pressure switch reaches the high pressure limit, then the compressor will shut off as designed; is there an open wire we should be looking for? Could it be a bad ECM? Again, the cooling fan will come on as designed without the A/C being on when the coolant temperature reaches the pre-determined point, so we're a little stumped. Any thoughts?
Thanks in advance, Chris :)
 
Could it be a bad ECM?
Again, the cooling fan will come on as designed without the A/C being on when the coolant temperature reaches the pre-determined point, so we're a little stumped.
As the ECM is correctly operating the fan when it should I would be looking for a fault on the input signal from the pressure switch , rather than a fault with the ECM itself
 
As the ECM is correctly operating the fan when it should I would be looking for a fault on the input signal from the pressure switch , rather than a fault with the ECM itself
Oz: OK, thanks; 2 things just to clarify:

1. I should be able to connect a test light to power and then touch the Dark Green wire (Circuit 992 to ECM Pin 11), and the test light should NOT light, correct? This wire should not be showing a ground circuit, correct?

2. If I disconnect the connector at the A/C fan control (pressure) switch, and the fan DOESN'T come on, then jump the 2 terminals together, should the fan come on at that point?

Thanks again
smile5.gif
 
The ECM shoud have a pull up resistor

I wouldn't test it with a test light though, If it's a old school test light it will pull to much current an LED type or meter should be fine...
I do not have my 88 shop manual anymore ( Sold the car ) .. but if I remember the fan control is on the High pressure side...

BRB
 
Stolen from another site

ECM monitors the fan switch on the high pressure line which opens at 220 psi and when it does, it grounds the Main Relay. Air flow cools the charge and when the pressure drops to 190 psi, the switch contacts close dropping the voltage signal at the ECM to 0. With that, ground is removed from the fan relay. You test the ECM by simply disconnecting the harness from the switch and that open circuit should signal the ECM to turn on the fan. You see if the switch is working right by hooking up a manifold gage set to see what the pressures are. Otherwise replace the switch - 12 Bucks or so. It's on a schrader, so you don't have to evacuate the charge to replace it.
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Advertise with the Corvette Action Center!

Double Your Chances!

Our Partners

Back
Top Bottom