Engine/Transmission (1994 - 1998) no ac in 105*

[Ahopper]

ok so i get up to go to work this morning and no ac. it is liek 105 out side and all that its blowing is hot air!!! i have been having a couple of problems with it . it used to be when i went to shut off the truck the fan would keep blowing? i would have to flip the ignition back on and off then it would shut off but besides that i have never had a problem with it befor i tried to turn it on this morning some guy ****** me off and i blew by him and my rps went through the roof like normal and then when i went to turn it on nothin. any help please im sweating like crazy

 

[Ahopper]

ok so i went out and trouble shooted my truck a bit. i now know that it has to be electrical because the compressor isnt even kiking on i replaced the relay and that did nothing. i dont know much bout ac but im figuring the clutch isnt kiking in. does anyone have a scematic or wireing diagram on how to fix this problem? thanks (yeah its still hot here in az)

 

[DavidC]

Could be low on freon and the low pressure switch is keeping the clutch from engaging. You would have to find the switch and jumper it out if that is your problem. Not sure where it is at on a 97. BTW I just looked at the thermometer and it is a crisp 96 fall day.



Dave

 

[surfbeetle]

Mine did that on my 95 a couple of months ago. Turned out the contacts on the relay under the hood were dirty. I cleaned the relay (and did the other relays as well) and all has been well. I would say that you need to check your relay to see if you have a good one and also check the wiring connection at the compressor.



When the engine is running and the A/C is turned on, you should be able to see if the center of the compressor pulley is spinning or not. As for the freon, you could go and get the system charged and see what happens.



If it were leaking you would notice a progressively longer time before it cools down and eventually it wouldn't cool down. You made it sound as if yours just all of a sudden stopped cooling, as did mine, so I am leaning towards the electrical. Good luck.

 

[Ahopper]

yeah it was ice cold yesterday so im thinking it electrical. davidc: your right it is only 96 but man when i get in my truck i know it isnt that cold lol

 

[Ahopper]

alright so now i put a pressure guadge up to the low pressure line in the ac and it read 110 psi!!!! what is that about. that is with the engin off and when i turned it on it stayed the same. please help!!

 

[DavidC]

Okay, since no one with a service manual for your year has responded I will let you know how a 99 compressor relay is (although you should really have a factory service manual for electrical diagrams). The AC clutch relay coil comes from fuse 11 10 amp in the cab which appears to get power from the ignition switch. This is the + side of the relay coil. The negative side goes from the relay coil to the PCM module. The actual AC clutch coil comes from the PDC fuse J 10 amp to the clutch relay then to the clutch. Negative side of clutch goes to ground. You can check those fuses and see if they are ok and check power to fuse 11 for power when truck is running. Hope this solves it. If not, let me know and we will check further, hope Dodge wired yours the same as a 99. Suppose to get down to 92 by the weekend. You could also remove the plug from the compressor and check to make sure you have continuity across the terminals with an ohmmeter to make sure you do not have a burnt out clutch coil.



Dave

 

[Ahopper]

thx davidc. i dont kow what it is because i tried to take it to acouple shops around here and they said because i have splived into a few wires ( i put a remot start, keeless entry and the tc lock up on it. ) i tried telling them that it wasnt part of the ac but they didnt belive me does anyone know if ther are any valves in the system that could bake the low end presure be 110psi when off? i really need the help i dont really know to much about ac work but man it is hot outside really miss the ac :{

 

[DavidC]

When the AC is off the pressures will equalize between high and low. Once the clutch engages the low side will get sucked down. I would not worry about that part but start checking fuses and power from the ignition switch at fuse 11.



Dave

 

[hsmith]

Your pressure is normal for a system not running. You mentioned earlier you sometimes had trouble getting the blower to stop running. Think you need to start looking there, ie, ignition switch maybe.

 

[NKenny]

Ahopper, did you ever determine what caused your AC to quick like this? I just bought a '94 with identical symptoms.



Thanks.

 

[jmy]

Ahopper,

If the compressor clutch is not operating it can be can be the pressure switch, or some other problem, but what I see more often with trucks that have 200K plus miles and heavy AC use is the clutch plate is worn and the gap between the plate and armature is too wide for the magnet coil to overcome.

You can see whether the clutch is engaged from the top. If it is not engaged the clutch plate on front of the hub will not be turning.
If the clutch is not engaged you can check If the plate gap is causing your problem (with the engine off) by removing the AC relay and jumpering across the normally open contact. If the gap is too wide the clutch usually won't engage with the jumper alone but if you tap the clutch plate lightly it will engage.
The clutch plate is usually shimmed to set the gap. Often you can remove one or two of the shims and the clutch will work again.
The clutch plate is easy to remove from the under the front of the truck. Takes about 5 minutes with a 13mm 3/8 socket and 2 flat blade screwdivers. The plate is on a splined shaft with a skip. It slips right off with a screwdriver blade on each side. You can then remove the shim(s) between the clutch plate and shaft collar. You'll need to line up the skip in the splined shaft to re-install the plate.

 

[fest3er]

The A/C on my '98 quit one day (strangely after I had Cummins Atlantic spill-port time the P pump; mere coincidence). The shop I brought it to bypassed the PCM and it has worked since. In my case, the PCM failed to 'turn on' the clutch. My compressor is original (227K miles, 9. 5 years, never serviced), and it works fine. Freon does leak out rather more quickly than I would like, but I expect that, at their age, all the seals and o-rings are pert near shot.

Shop: Mr. Murphy, it looks like you've blown a seal.
Me: Hey! Just fix the darned thing and leave my personal life out of it!
[Adapted from "Wet Dream", album "White Boy Rapp", by Kip Addotta. ]

As I recall, there is +12V feeding the wire that passes through the PCM, the low pressure cutoff switch and the high pressure cuttoff switch on its way to the compressor clutch. If any one of these fails to close the circuit, the A/C won't work. Oh, yeah, first ensure that the PDC is supplying +12V to this circuit!

Unplug the low pressure cutoff switch connector with the engine running and the A/C enabled. You should see +12V on one pin (this is through the PCM) and near ground on the other (this is the clutch side). Not even close to ground? A/C clutch mechanism is the likely culprit. No +12V? PCM is not engaging its relay.

I can almost guarantee that nothing will be harmed if you unplug the low pressure switch connector and apply +12V to the clutch side; for that matter, you could safely apply +12V directly to the correct pin on the clutch for a few moments. If you hear the clutch engage (click), you are on your way to determining the cause of the failure.

One possibility is the low pressure switch has failed; you can remove it, and clean it with a few spritzes of carb cleaner and bang it on a workbench a few times (to bounce the spring and switch). Then make sure all the carb cleaner has evaporated and put it back on. If the A/C now works, buy a new switch, because it probably needs replacing.

The high pressure switch should almost never disengage. Whilst you *can* bypass it, I don't suggest doing so. If the pressure gets too high, you'll hear a loud, discomfitting noise from the compressor. Trust me, I know. Hmmm. I wonder if that's the source of my Freon leak? More properly, I would expect the system to be filled only to the point where the low pressure side is sucked down far enough to shut off before the high pressure side gets too high.

If you have determined that the circuit to the clutch is good *after* the PCM, you can cut the wire between the PCM and the low pressure switch and run a new wire from the PDC. This is how mine has been set up for 3-4 years now, and it's been working great.

The PCM relay is needed only to allow the PCM to disengage the clutch; typically this happens when climbing a steep grade and the go pedal is matted for a 'long-ish' period. With the mighty Cummins, we never notice when the A/C is running - it's such a low percentage of the engine output - so there's no need for the PCM to control the clutch; it is quite safe to bypass the PCM in this case. But do be sure the high and low pressure cutoff switches are functional; they *are* important.

N