benp10

So the truck was running fine and never stalled.. I fix the a/c... New compressor, dryer, orfice tube.. It was fine just idling while I was charging it with refrigerant then I took it down the road and when I come to a stop it gets to idling real low and eventually dies.. I've figured out it doesn't stall without the air on so I've been coming to a stop to wait on the light to turn green and when I feel it start to idle down I'll flip the AC off and it's all good...I can watch the voltage drop gradually lower and lower until it stalls, so I replaced the battery. It was from 2011 so i figured that was the problem but it still does it.. It just seems like the AC is pulling a lot of juice...Thinking of replacing the alternator next.. Anyways just wanted to see what anyone else thinks...thanks..

Martian

AC should pull barely any electricity, really. The compressor is all mechanical except for the pressure sensor and the clutch. Sounds like you have an alternator problem.

benp10

Also it only happens when sitting still.. Like waiting for the light to turn green for example..

GhostriderI

Which Carb do you have? might want to adjust curb idle with warm engine and AC on to about 650rpm to 700rpm and see if it still stalls. Mine was doing that as my kick-up for the AC was not working and is no longer available. This was my workaround.

benp10

it's the electronic fuel injection.. Can you adjust that? I'm not sure and don't know much about carbs..

GhostriderI

Oh ok. I was thinking you had a carb engine, 85 was the transition year 302/5.0 was the only injection engine (If I remember correctly) that year in the F-150. You will have to check your emissions sticker under the hood for your specification. Check your curb idle is correct, if it is low that can contribute to stalling at idle

3rd-cst-thumper

Definitely change the alternator. Mine was doing the same thing when I bought it. Would run fine until I turn on the AC, then it would kill. I got a reman off of amazon for $40 and it solved the problem.

benp10

Well the folks at o Reilly's say my alternator is "good" putting out 40 amps? Does that sound about right?

3rd-cst-thumper

That's the thing with electrical components, often times they test fine but don't perform under a significant load.

Use a multimeter to check the battery w/ key off. It should be between 12.5-13.0 volts. Start the truck, volts should rise to 14 volts within a minute or so. Turn on all accessories (headlight, AC, radio) and check voltage. It should be hovering between 13.5 & 14.5. If not the alternator is bad.

Does the battery drain when the truck sits with the motor off?

benp10

no it doesn't drain.. The battery I replaced was from 2011 and I sat in it at work on my breaks and listened to the radio with the truck off and it would fire right up 3 or 4 hrs so I think even that battery was still good.... I'll check all plugs and check for any corrosion and make sure I have good connections.. Then if I still have issues replace the alternator.. The aftermarket ones are less than a hundred bucks so it'll be harder to change than to come off the wallet and I'm always down with that