i put this question on ac/heating forum, but got no replies, so i thought i would give this one a shot.
i recently converted ac to r134a in 88 f150 with 300i6. used interdynamics kit, and air is cold,compressor is quiet. however, i am having some idling and stalling problems. it only happens occasionally, and does not seem to be related to how hot or cool it is outside.
this truck was purchased used so i have no idea how long the ac did not function ( it was empty).
all that said, here are my questions:
the owners manual says to turn off the ac before turning the ignition off to prevent dieseling because of the "device" which compensates for ac load may cause run on.
on a fuel injected engine what is this device ,and where do i find it? and does any one think this might be my problem if this "device" is defective or inoperative?
if not this then what? too much r134a? bad compressor?
btw, i did turn up idle slightly, but it still did it. thanks for any help!

 

The conversion should not be the problem, unless you overcharged the system. Check your high and low presures and advise as to what they are. Should be at idle around 40 psi on low and 225 to 250 on high side, if you are higher then you have too much freon. When you converted the system did you vacuum out before your recharged? Please in detail tell us what you did.

The idle is controled by the Idle Air Valve. This through the processor should idle up the motor when the a/c is on. If the valve is bad or clogged it will not function properly. Let us know for further

Dave

http://a2ztowing.homestead.com/a2ztowing.html

 

thanks deleontow for reply. i did vacuum system and changed the accumulator and orifice. the pressures are in range you stated. i will check the idle air valve this weekend and get back with results. thanks again.

 

deleontow, i checked idle air valve, and it seems ok. tuck was driven 3 days straight , about 80 miles each day with no problem until today.
it would stall when stopping for light or stop sign. it only occurs occasionally!
i am going to borrow some other gauges to see if my readings are accurate. any other things i should look for? the ac is still cold and quiet. thanks for any suggestions.

 

I am having the same problem with my 91 F-150 302. I have also converted to R-134A, but would agree with the others that say this is not the problem. I just did a tune up (plugs, wires, cap, rotor, pcv, Air Filter, oil) I did notice a little improvement. I suspect the I.A.C. valve, but don't want to spend 60 bucks to find out. My will still stall out even if the A/C is off. My will spit and sputter for about 10 seconds then it smooths out. If it doesn't die during those first 10 seconds, everthing is fine. I am also suspecting EEC or fuel injector, fuel pressure regulator problems. Hopefull someone know more about those than I do.

 

mudflap, my stalling is only with ac on. but, i bought truck used and ac wasn't working when i got it.
i am wondering if anyone knows how to bypass the iac valve electronically to see if idle stays steady. this would isolate the iac as the problem i think!

 

There are a few electrical tests for the IAC valve in the haynes shop manual for our trucks. Have you tried cleaning it? When you start your truck after it has cooled off, it should idle high to begin with (1500 - 2000 rpm) and the idling should gradually drop to it's normal idling of around 700 - 1000 RPM. This is the IAC valve controlling the idle, meaning it works. It may just be dirty or it's something else.


'92 F150 XL 4x4, 5.0L AOD, Headers, K&N Air Filter, 3.55 Gears, 31x10.5x15 Tires.

 

The Chittlins Manual I have say to test the IAC as follows:
1. Key Off
2. Disconnnect IAC
3. Use Ohm Meter to Measure resistance between connectors on the IAC. ( Note there is a diode in the IAC so if you get nothing on the Ohmmeter, reverse the leads)
4. The resistance should be 7-13 Ohms, if not replace IAC.

You can also try this:
With engine running, disconnect the IAC. The engine should stall or idle speed should drop a lot. This test will tell you if your PCM is at least trying to control the IAC. If nothing changes check connection between PCM and IAC.

It would be very difficult to electrically bypass the IAC. In other words connect a voltage source, or short a pin to ground, because the PCM sends a duty cycle signal to the IAC. Which means the PCM rapdily turns the IAC on and off depending on the laod on the engine. This would be very difficult to simulate with-out some pretty fancy equipment.

As for the A/C only, this is when I first noticed my problem. I would turn the AC off, and it would work fine. Now the problem shows up, even with the AC off. It does better right after a tune-up. But it is still there. I am thinking about pushing the whole thing into the lake and starting over.

 

I agree that the a/c most likely isn't the cause. I have a similar problem with my '90 351 Bronco. It will idle just fine most of the time but sometimes when it has been idleing for a while at a long light it will begin to surge. If I check it by throwing the truck into neutral I can stop it. I have checked all the circuits and switches and they check out with in specs. I did however find a hose to the PVC valve that I suspect was causing a leak and I think that a leak might eventually prove to be the cause, but you would think a leak would be consistant. I bought a new computer because I wasn't getting any trouble codes no matter what I tried. The new computer gave me codes but didn't solve the surge problem. If you figure this out let me know and I'll do the same for you if I figure it out.

 

OK guys did a little reserch on these problems, seems there may be deposits on the injectors which would require them to be cleaned. see ford tech bulletin 93-11-4 dated 05-26-93 (Rough Idel or stumble caused by injector deposits). Appartly the injectors which are supposed to be deposit resistant are not. They suggest you clean the injectors and tell you how on tech bulletin 91-19-3 dated 09-18-91 (New method of Fuel Injector Cleaning). They suggest you buy a service kit to attach to the fuel system and clean the injectors. should anyone like me to fax them copies of these bulletins please call me at our phone number which you can get from our web page.

Dave

http://a2ztowing.homestead.com/a2ztowing.html

 

hey everybody, thanks for all responses to problem with stalling after ac conversion.
the problem seems to have been a little of each thing! the main problem with the idle air valve was corrosion at connection. i cleaned this up and the resistance reading fell back to correct range. i also thoroughly cleaned inside of valve.
truck runs smoothly and stalling has subsided!
thanks again!!