I need an AC guru - Northern California Ford Owners

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Posted by mtbaughs (Member # 4052) on :

I am having problems with the air conditioning in my dodge and need someone who works as living doing this to help me out or someone who really knows their stuff with regard to this. Whats happening is the compressor clutch isn't kicking on at all. The things I've checked so far, the relay's for the compressor clutch, rad high relay, fuses all checked out good. I know there is a pressure switch which will only kick the clutch on if certain pressure is seen in the system. So I checked what I think is the low pressure port with a gauge and got 100 psi which is way more than the specified range of 25-45 psi. What might be going on? Thanks

[ April 29, 2004, 07:50 PM: Message edited by: mtbaughs ]

Posted by 94gt (Member # 3060) on :

has it sat for awhile? My stang wasnt running since Dec, and the pump only moved when I rotated it a bit, in an effort to keep the seals a little lubed up.

I had it almost all the way drained a few months back, and when I checked it last weekend, BAM! 120~psi [Eek!]

I crapped my pants, drained all the pressure out of the high and low pres. sides, and then reserviced it.

I talked with a buddy of mine that does HVAC, and he normally just jumpers out the low press switch, and then services the system... with the car running and the a/c on max. works like a dickens!

I hope this helps [patriot]

Posted by mtbaughs (Member # 4052) on :

Thanks bud, well the car is pretty much driven daily. I noticed a month or two ago that it wasn't blowing cold air anymore. Especially the last few days it's been hot as hell so I really want to figure it out. I've never drained or serviced the system. I might try and jump the pressure switch now if I can figure out what the three wires going to it do. I turned the compressor clutch by hand a few time and no change. It never kicks on. I'm wondering if it is seeing so much pressure because there is water in the lines do to the evap not functioning properly. It's just one of those things I hate to spend money on because ac isn't a must have thing but it looks like an AC guy might be needed soon with the weather

Posted by 88bird (Member # 1424) on :

The 100 psi is static pressure and thats good, the 25 -45 is on and off pressures for the switch. Do you have voltage at the pressure switch? With out a schematic it's hard to diag, does the compressor run in defrost mode? If so you may have a bad climate control switch.

Posted by mtbaughs (Member # 4052) on :

Well the 100 psi is with the car running and ac on. The range 25-45 psi that I determined to be the specified range is based off what the AC recharge kit says is the specified range. I am getting 5 v to the pressure switch of which has 3 wires. One 5 volt wire, one signal wire and one ground. The compressor clutch doesn't come on in any position even defrost. Heres the thing. I disconnected the battery and re-connected it and noticed right off both radiator fans kick on but only for a second before shutting off. I wasn't able to run up there to see if the compressor clutch kick on with them but I have been told that this car's ac is tied into those fans kicking on. The car I guess has a high speed and a low speed fan. I wonder if something there is causing an issue

Posted by 88bird (Member # 1424) on :

The fans come on with the a/c to cool down the condenser. Doubt that is the issue. usually the pressure switch is only two wires. Whats the year, and model. The switch you are talking about sounds like it is tied into the engine management system, cause it has a 5v refrence.

Posted by mtbaughs (Member # 4052) on :

'01 dodge intrepid 2.7L I think the way the switch works is basically the ECM checks it for the right pressure, if it's good the ecm sends a signal to the BCM to turn the compressor on. This is just my guess.

Posted by 88bird (Member # 1424) on :

Sound about right, Need dodge specific info for climate control electronics,

Posted by mtbaughs (Member # 4052) on :

This is the best online ref I have seen and list everything but I have trouble making sense of it, maybe you can figure it

http://dvms.dvusd.org/02lhe.pdf

Posted by mtbaughs (Member # 4052) on :

Update:

I checked for voltage on the positive lead running to the compressor and it shows a good 13.9V while the car is running with the AC on. I checked the ground for the compressor as well by putting the negative side of the DMM to the lead and the positive side to the battery. Normally I would expect to see the normal battery voltage but I was only getting 4.88V through this ground. I wonder if this is causing the problem because the ground isnt showing full battery voltage?

[ April 30, 2004, 02:50 AM: Message edited by: mtbaughs ]

Posted by 88bird (Member # 1424) on :

The ground will only show full batt voltage if it has an open ground. With the red dmm lead on the a/c coil ground, and the black dmm lead on b-, there should be less than 1v. If you have 4.88 volts, sounds like a bad ground. Without a wiring diagram, Need to find out if it is power, or ground side switched. I'll see if i can find a diagram.

Posted by 88bird (Member # 1424) on :

It's power side switched. If you have Batt voltage at the a/c coil and 4.88 volts on the ground wire for the a/c coil, then I would say you have a bad ground. What this is telling you is that it needs 4.88 volts to complete the ground
and it should take 1v or less. So you can try to splice in a new ground and see what happens.

Posted by mtbaughs (Member # 4052) on :

Hey, thanks so much for your help. I am going to try running another ground for that lead. One other thought I had was if I was losing that ground because of an internal issue within the electrical side of the clutch. Running another ground should tell me that. Thanks again [patriot]

Posted by mtbaughs (Member # 4052) on :

Ahhh satisfaction finally. Ran the new ground for the AC compressor clutch and bam success! The compressor clutch cycles on and off as it should. Damn it's always nice to figure this shit out without wasting money in the shop. Thanks 88bird for the help along the way. I am thankful to have some good advice since AC isn't performance it's not my strong point. None the less it's ice cold inside the car again ready for summer. [worship]

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