I have a 2000 Ram 2500 V8 5.9L gas AT, that hasn't had a/c since the day I bought it 9 years ago.

I decided to change that, and so installed a new evaporator, heater core, accumulator and cycling switch. Condenser isn't visibly clogged and radiator was new about 6 months ago.

I pulled a vacuum, no leaks, and charged the system with 32ozs R134a using a gauge set.

With compressor running, low side is 40psi and high side 220psi but air is only cool, not icy cold.

When driving with air diverted through face vents, air will randomly be diverted to defrost vents for perhaps 30 secs to 1 min and will then revert back to face vents.

With truck idling, this does not seem to happen. I hoped to see whether it would coincide with compressor dropping out or kicking in, but it won't do it when stationary.

Does anyone have any idea what may be going on? I'm out of ideas.

Thanks in advance!

 

Try a search of the forum for "wild vents" for hints on how to solve that annoying switch to defrost problem. It's very common for these things, all older vehicles that vacuum actuate mechanical parts, really, to develop leaks that cause vacuum motor weirdness. In these it's often a check valve or two, perhaps in addition to a leaking line. It's always a cheap fix, but sometimes a PITA.

AC pressures have to be compensated for atmospheric temperature and humidity to be meaningful... Snag the factory service manual for your 2000 Ram from the FAQ/DIY section if you don't already have one -- the diagnostic procedure it calls out is good enough to get the job done.

 

I found the Factory Service Manual and downloaded it, thank you for that.

Even allowing for temperature today, my pressure readings are good according to service manual.

 

On your truck, there is a little electric motor that moves the temp door. It's on the bottom side of the heater box, above the trans tunnel, just to the passenger side. Two screws and an electrical connector.

Ignition on, turn the temp dial to the middle of the range. Count to ten, turn the ignition off. Drop the little motor, and check the coupler between the motor, and the shaft for the temp door. They are notorious for cracking, and not giving you full range of movement of the door. HeaterTreater.net has the fix.

 

Thanks for the info - unfortunately, the way my plenum box is installed, one of the temp door motor screws is hidden by the trans tunnel. Only way to access that screw is to swing dash away and unfasten plenum box.

Having just got it all put back, that's something I'd rather not do

 

If you cut the carpet a bit, you can get to it with one of the 90* screwdrivers. Yeah, it's awkward, but, doable.

 

I don't know if yours is different to mine, but I had to tug the carpet to free it - the motor is sitting about 1/8" above the trans tunnel, no room to get any tool in at all, even a 90 degree screwdriver

 

Can you post a pic? There should be *relatively* easy access to it......

I don't have one at all. Cable operated up to 99.

 

I am just watching the video by HeaterTreater that shows what's involved. There's actually a rubber padding under the carpet that I didn't realize needed to be removed too.

I'm going to have a go at dropping the motor tomorrow and seeing if that's the problem. Thanks for all your help, I'll let you know how I get on..!

 

I got mine done. Just had to work at it a bit. What worked best was a ratcheting doohickey from hobo freight. The kind you can put a phillips or straight in. Like this

http://t.harborfreight.com/8-piece-r...ver-92630.html

Or you may even up just using the bit and a small crescent to turn it while you hold it in place with the other hand.