Son has a 93K 86 F150. We've dealt with fuel feed issues & eliminated them. When the truck is cold in 90° temps, when the AC button is in, everything is fine. As soon as you move the fan switch it starts bucking & jerking, cut it off, drives smoothly.

Anybody suggest a solution? I seem to remember something about an AC cut-off switch to conserve fuel, but can't find any info.

Any help is appreciated.

 

Sounds like you may have a ground problem. Make sure you have the factory ground hooked up from one of the bellhousing bolts to the firewall. There is another important ground over at the battery. It's a small wire coming directly off the negative bat terminal and goes to a connector and then into the harness. This ground being around the battery likes to corrode.

 

What engine? Is this fuel injected or a feedback carb?

Two things come to mind. In both cases, the extra electrical load of the AC compressor may be causing system voltage to drop due to an iffy connection. I'd suggest connecting a voltmeter so you can watch the system voltage when the engine acts up. The cigarette lighter would work as a place to connect your meter:

1) Ground G701 under the dash may be marginal. Details here of how to check it by using a test jumper to the outer shell of the cigarette lighter:

https://www.ford-trucks.com/forums/1...vac-is-on.html


2) A funky ignition switch. A super easy method to check it is here:

https://www.ford-trucks.com/forums/1...on-switch.html

 

Sounds like the A.C. was already on, but the fan being turned on messed it up. If I am reading that right.

 

I don't think the compressor will come on till the fan is turned on.
So if the compressor has an issue like partly sized that would be a problem.
Pull the belt to the compressor and try again.
Dave ----

 

According to the diagram below, as long as the selector switch on the right is not in off, the blower is always running. There is no off position on the speed switch. So the blower was running in low speed if the selector was in A/C already. You can see on the left selector, the compressor is on in A/C Max, A/C, Mix and Defrost.

 

Factory or Dealer air?

 

Bought used, 2nd owner, Factory air presumably, as the truck is maxed out accessory wise. Long bed, dual tanks, power windows, etc. Will be going thru the checks as recommended over the week-end. Ground issue makes a lot of sense.

Appreciate all the input.

 

I was just curious, you said when the ac button is in, and none of what you said fits with anything I remember, or what I'm looking at with both of my trucks.

 

I was thinking the exact same thing, I am not aware of any "buttons" controlling the HVAC (or anything, for that matter)....?

Pictures would tell a lot.

 

Bumpity bump!

Was this ever resolved?