AC blows cold when truck moving, warm when idle

[TrexMex]

Last sunday, I went trailing with a couple of friends. It was about 120 outside but because we were pretty much climbing about 3000 ft off-road I didn't turn the AC on, didn't want to overheat the engine. We stopped to take a break and soon after turning the engine off I noticed a leaking sound coming from the engine bay; popped the hood and looked for it but to be honest between outside temp and engine temp I couldn't get near enough to isolate the noise to a single component, but I know it came from around the compressor. So my first thought was AC just wasn't going to work at all... I turned it on and noticed it was blowing cold air so to be honest I didn't pay attention until yesterday when we hit the 120 mark again...

I guess my question is what would be the first step to take here? just get the compressor serviced and checked for leaks? If I'm to do this myself this would be my first time messing with the AC system (not that I haven't messed with pretty much everything else in my prior ranger with good success) and I want to learn how to do it... It's a '94 so would it have R134a or R12?

Thanks for any guidance you can give me on this guys!

EDIT: forgot to mention... temp gauge is right in the middle all the time...

PS... Its great to be back after 6 months of absence

 

[TrexMex]

anyone??

 

[shadetree]

Are you saying the a/c no longer blows cold air when it gets very hot outside? I'm not really following what you are saying. When you turn off the truck, and the a/c has been running, you will hear the pressure equalizing in the system. This is normal. More info would be helpful. A/c systems can be complex, and some knowledge is required to work on them. shady

 

[TrexMex]

Are you saying the a/c no longer blows cold air when it gets very hot outside? I'm not really following what you are saying. When you turn off the truck, and the a/c has been running, you will hear the pressure equalizing in the system. This is normal. More info would be helpful. A/c systems can be complex, and some knowledge is required to work on them. shady

well got rid of the first problem, recharged the system to spec pressure and voila, and thanks for the other advice that's exactly what I hear when turning off the truck... some hissing noise then it goes away, this only happens when outside temp is around the 100s...

thanks again!

 

[TrexMex]

So I found out that when at an intersecion, compressor engages and disengages a lot, meaning I get warm air and cold air a lot..... problem goes away when the truck is moving... what could be causing this?

 

[ZYTHUM13]

You might need a new fan clutch. Not only does it cool your radiator but also your condenser.

 

[v8318cid]

If you're getting a great deal of cycling at idle when its in excess of 100F outside, you're probably getting rapid cycling of the compressor due to high pressure (as opposed to low pressure). I have a 92 which does not have a high pressure cut out switch, but I'm thinking that when Ford convered to native 134a systems, they may have swapped out the pop-off valve with a high-pressure cut out switch (rear of the compressor, possibly on the hose manifold). If the pressures are getting too high, the compressor will shut down to prevent blowing a hose. I'd say you are either overcharged, or more likely, have insufficient air flow across your condenser. If you haven't already resolved it, you may want to clean your condenser coils and check your cooling/rad fan as well. Hope that helps (and wasn't too long...).

 

[BRUTUS_T_HOG]

your fan in not working

 

[TrexMex]

If you're getting a great deal of cycling at idle when its in excess of 100F outside, you're probably getting rapid cycling of the compressor due to high pressure (as opposed to low pressure). I have a 92 which does not have a high pressure cut out switch, but I'm thinking that when Ford convered to native 134a systems, they may have swapped out the pop-off valve with a high-pressure cut out switch (rear of the compressor, possibly on the hose manifold). If the pressures are getting too high, the compressor will shut down to prevent blowing a hose. I'd say you are either overcharged, or more likely, have insufficient air flow across your condenser. If you haven't already resolved it, you may want to clean your condenser coils and check your cooling/rad fan as well. Hope that helps (and wasn't too long...).

Thanks, it was very descriptive actually.... I'll check the refrigerant pressure tonight; what would be the pressure I should be shooting for at, say, 90-100F? Yes... it's still pretty damn hot at night around here...

About the condenser coils, I'll check 'em out as well. I changed my fan clutch a week ago so that's not under suspicion.

Thanks again for all the help!!!

 

[BRUTUS_T_HOG]

at 90-100 degrees outside temp you shuold see about 110-120 psi static pressure with a fully charged system

 

[TrexMex]

at 90-100 degrees outside temp you shuold see about 110-120 psi static pressure with a fully charged system

Low pressure side?

 

[DragRag]

40 psi low side while operating. Thia is an approximation, and may vary depending on ambient, cabin temps, and percentage of charge in the system.

 

[oldjohnny]

So I found out that when at an intersecion, compressor engages and disengages a lot, meaning I get warm air and cold air a lot..... problem goes away when the truck is moving... what could be causing this?

I got the same problem.

When the outside temp goes over 100 F, the compressor clicks on and off at idle. Reeving the engine above 1100 RPMs fixes the problem (or like you said, getting the truck to move again)

Please let us know whenever you fix your problem.

 

[BRUTUS_T_HOG]

Low pressure side?

high or low.. with the engine off.. a properly charged system will be about 10-20 PSI above outside TEMPERATURE.

if you're pressures are ok and it only cools while in motion, you have a problem with your cooling fan. or the outside temperture is too high for the cooling fan to work efficiently

 

[TrexMex]

I got the same problem.

When the outside temp goes over 100 F, the compressor clicks on and off at idle. Reeving the engine above 1100 RPMs fixes the problem (or like you said, getting the truck to move again)

Please let us know whenever you fix your problem.

http://www.therangerstation.com/forums/showthread.php?t=55527

Thread started in V6 4.0 forum with same subject... Good answer by AllanD in there.