Stalling when A/C turned on

Asked by Aug 17, 2016 at 10:50 PM about the 1987 Ford F-150 STD Standard Cab SB

Question type: Maintenance & Repair

I have a 1987 ford f150 4.9L straight 6. My truck
idles fine when the a/c is off but as soon as I push
the button to turn on the a/c it dies only at idle.
When I go down the street or high way it works
great. But when I stop it does. I have cleaned the
idle air control valve and throttle body and the
truck runs better but has the same issue with the
a/c. I've been researching this issue and still
haven't found anything on this. Does anyone have
any idea whats going on here?

3 Answers

31,755

is the a/c solenoid clocking on?? > www.google.com/search? q=1987+Ford+F- 150+a/c+solenoid&espv=2&biw=1024&bih=729&source=lnms&tbm= isch&sa=X&ved=0ahUKEwiWqIuf_snOAhWG7CYKHZdMBskQ_AUIB ygC#tbm=isch&q=1987+Ford+F-150++a%2Fc++idle+solenoid

118,555

Sometimes the ECM forgets the rig has A/C especially on the old OBD 1 systems, so try this, disconnect a battery cable and turn on the headlight switch, wait at least a minute, turn off the headlight switch, reconnect the battery cable and start the engine and a fast as you can turn on everything electrical especially the A/C and fan, let the idle stabilize and let it idle for about a minute, then turn everything off and shut the engine down, wait about 2 minutes and fire it back up and then see if it will hold the A/C idle, if it doesn't then there maybe a problem with the IAC unit it may not be able to open up any further than the base setting. HTH

28,325

Another condition I have seen is with an aftermarket AC system installed. There is nothing to signal the PCM that there is an additional load. You may be able to reset the Idle parameters after cleaning the Throttle body and plate. The proper way is to disconnect the Battery - clean the Throttle Body - Reconnect the Battery - Start and run the Engine at 2500 RPM until Operating Temperature (about 3 Minutes) - Allow the vehicle to Idle In Drive for about 2 minutes - Allow the Engine to Idle In Drive with all accessories (including the AC and Headlights) on for an additional 2 minutes. You are re-teaching the PCM how to Idle under different conditions.

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