Ram Truck A/C Troubleshooting

I was driving on the interstate last week with my defroster going (1999 Dodge Ram 1500 with 5.2L engine, manual tranny) when my windshield starting fogging up severely. I had to open my window to get the
windshield to clear. I knew immediately my a/c was working properly.
I only have a Haynes service manual to go by and of course it not only doesn't go very in depth on trouble shooting the a/c system, but the schematics for the a/c clutch relay is not the same as the relay in my truck. I did check the fuse (in the PDC under the hood) and substituted relays from other circuits (identical part numbers) to no avail. Today, I went out and tried jumping the cycling switch on the accumulator to see if the clutch on the a/c compressor would energize (it did).
With this information, could someone tell me where to go from here to troubleshoot? At this point, I'm figuring I've either lost the a/c charge or the cycling switch is defective (but this is strictly a guess).
Thanks,
Dave Young
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On Tue, 27 Feb 2007 16:38:54 GMT, Dave Young

Right off it sounds like a leaking evap coil. I had to have mine replaced on my 2000 Ram about two years ago. You can do it yourself, but there is a lot of labor to it. Cost for replacement at a dealer is about $1200.00, I got mine done by an independent for about $600.00. Cost of the new coil is about $100.00. Good luck.
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Your heater core is probably leaking. Do you smell antifreeze?
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It's not a heating issue....when you turn your defrosters on, it also turns on your a/c system to help get rid of the moisture. My a/c compressor isn't kicking on the way it should. With the diagnostics I've done so far, I'm thinking I'm probably low on refrigerant.
If it is a leaky evaporator, I'll replace it myself (unless there's something tricky about it (and there shouldn't be) and have a garage evacuate the system (requires a vacuum pump that I don't have). I should be able to charge it myself. I used to be trained in HVAC through the military, and at one time I was quite good. I was responsible for the HVAC and refrigeration systems on Coast Guard cutters. However, that was several years ago, and I've forgotten so much.
Thank you for the answers so far!
Dave
Roy wrote:

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two ways to find out if it is leaking quckily
Put dye in the system (not reccomended) Or get a electronic refrigerant detector. If the detector smells refrigerant it will beep at you and closer you get to the source the louder it gets. Though you will still need to put gages on it to see it if has pressure in it.

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Probably you've had a slow leak for a bit, and it finally got to the level where the low-pressure cut-off switch popped. All that warm, humid air blowing onto your windshield caused the fogging.
If you have a local shop with a R-134 detector, have them stick the probe in the floor vents while you run the blower. When I recently had a suspected leaking evaporator, I had a local shop verify this, which took all of two minutes.
Alternatively, you can get some recharge cans of R-134a, and some tracing dye. Inject the dye into the system, followed by the 134. Run the A/C for a couple of days, then take a black light to the system, and see where the leak was. A leaking evaporator will show up at the condensate drain, on whatever the water hits when it drains out (sometimes a suspension member, sometimes a puddle on the ground).
And no, there's nothing complicated about replacing the evaporator - just a big PITA. Once the system is evacuated, the cooling system has to be drained (not completely - just enough to lower the level below that of the heater hoses going through the firewall). In fact, I'd just put a bucket under the firewall, disconnect the heater hoses, plug 'em, and blow some compressed air into the heater core to clear it out.
The real fun comes in pulling the dash, though this job can be severely shortened, as well. Remove the knee blocker panel, and remove the piece of dash frame at the bottom, so that the steering column can drop freely. Drop the column (two bolts hold it to the firewall mount) onto the seat. Remove the five bolts along the defroster grids that hold the dash to the firewall, and remove the two bolts behind the side kick panels. This will free up the dash. You should have enough room to rest the passenger-side of the dash on the seat, giving you enough room to access the HVAC unit. If not, disconnect the wiring from the bulkhead connector (low on the driver's side) and other surrounding connectors, remove the steering column connectors, and any other wiring (radio antenna, etc)., and haul the dash out of the vehicle.
No matter how you do it, it's not a particularly fun job.
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Thank you for the replies. I ended up getting rid of most of my HVAC equipment years ago, including an electronic leak detector. Like Tom suggested, I believe there is a slow leak. At this stage of the trucks life, I'm not going to pull the dash (shudder! Been there, done that...). I did look at the system to see if there was something obvious (oil traces, rock damage to the condensor, etc), but didn't see anything. I think I'm going to buy some refrigerant, charge the system, and see how long it lasts. If it goes rapidly, I'll think about plan "b"; trying to find out where the leak is. At the price R134A is, I can put a lot of refrigerant in before it's cost effective to put in big money into it. For that matter, the refrigerant could be lost through the seals of the compressor.
Dave Young
Tom Lawrence wrote:

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On Tue, 27 Feb 2007 23:07:36 GMT, Dave Young

the light, goggles, and dye. add the dye, recharge and then in about a week , at night start looking for the leak. First place I would check is the condensate drain coming out of the firewall, the other obvious place is at the compressor seal.You can't miss a leak, it will show up bright yellow/orange with the light. JMTCW
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Maybe you can find someone with a set of gages for the new 134A, and see what kind of pressures in the system. I've got gages and some of the new non-freon 134A, but I remember we're a couple hours drive away from each other.
Check your local auto parts store. I'm remembering a charge kit I saw awhile back that had a cheap low side gage on it. I think the new 134A is unrestricted, so that's not an issue. Amazing all the AC stuff they have at auto parts stores.
Many of the older leak detectors won't detect the new 134A, so you likely made a good choice to get rid of it years ago.
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Christopher A. Young
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Does Dodge use a special size port adapter for charging the A/C? I bought a kit to do it that included a gauge, hose and port connector (my gauge manifold would require adapters to attach the hoses, plus an adapter to pierce/use the can) and I busted the stupid plastic connection as it was slightly too small to fit the charging port. I'll get my money back, but I don't want to repeat it. If I need to go buy the adapters for the gauge manifold, I'll do that....
Dave
Dave Young wrote:

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Nope, uses standard R-134a fittings. You did hook up to the low-pressure port, on the metal line alongside the passenger fender, and not the high-side port, near the compressor, right?
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No...I did the right port...as you said the one that's on the metal line, had a black plastic cover over it (removed it to charge of course!), just behind the radiator support on the passenger side. I thought the plastic fitting on the refill kit was going on way tighter than it should, then it cracked, and one of the parts that grip the charging port came off the plastic fitting. Back when I did this kind of thing occasionally, I bought adapters and stuff from NAPA. Probably what I should do now.
Dave
Tom Lawrence wrote:

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Put an AC gage on the low side, and see what the pressures are. If zero, then you've lost your charge. Not sure about the new stuff, but the vehicles I've serviced need about 35 PSIG to make the compressor come on, and then it kicks off about 20 or 25 PSIG.
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Christopher A. Young
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Chris,
Thanks....I was curious about the cut-in/cut-out pressure. I still need to go buy an adapter for my gauge manifold.
Dave
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