Hello everyone.

So my mom has a 2010 ram 1500 5.7L v8 she got from my (deceased) step father, the truck has been perfect all the way up to 192,000 miles (Just recently developed a slight knock in the top end that I'm working on addressing). But the past year or so the AC has been somewhat intermittent and has gotten worse and worse. I've worked on AC systems before so I'm not entirely new to them (I fixed the AC in my old 95 ram and my 2003 ram) but I would NOT say I'm an expert. But this specific one has been driving me nuts... The AC is extremely intermittent. When it is running it's cold, holds good pressure, but sometimes it just shuts off and doesnt come back on at all, restarting the truck seems to have no effect (sometimes it does), when the compressor shuts off the low side pressure builds up super high to around 80-90 PSI and the clutch just doesn't come back on. I've evacuated, pulled a vacuum (doesn't lose vacuum if I leave it for a few hours), and recharged it twice with 26 oz's of r-134a refrigerant (sticker under the hood says 1 lb 10oz for 5.7L), each time it works for a little while (about 20 minutes) then shuts back off and the low side pressure just slowly climbs up really high... At around 88F ambient temp it'll have around 38(ish) PSI low side and 180 high side, which I thought seems kind of low, so I added a quarter-to-half a can and the pressure went up to about 40 Low 200 high but I didn't want to overcharge it, and the AC got quite a bit colder, but it just shuts back off and stays off and seemingly never comes back on. The electric fan works when the clutch is running, but it shuts off when the clutch stops and when I check the harness, the clutch is recieving no power (verified with test light probed into plug), the plug also has perfect ground. What's weird is if I jump ground and 12 volts directly to the compressor the fan kicks back on and then the harness has power again, so I plug it back in and it works again for a while but eventually just shuts off. I can't find a low pressure switch on the system and I heard it's built directly into the TIPM? I can't seem to find a relay in the fuse box for the AC compressor either... I found a 40 amp fuse, and it's fine... It's quite hot here in Georgia and she can't drive anywhere without AC (she has some medical issues). Any help/advice would be GREATLY appreciated!

So to recap:
-Clutch is intermittent
-Electric fan works and runs when compressor runs
-When the clutch decides to turn off, the harness plug has no power
-Checked fuse, can't find relay (anyone know where it is..?)
-AC comes to life when I jump power to the compressor for a second (for a little while)
-Pressures when running seem fine (if a little low?)
-I checked the power wire to the best of my ability (which isn't saying much), can't find any damage...

Thanks again for any help.

 

I'm kind of thinking maybe the compressor has gotten weak, which would explain the lower pressures, but I don't think it could cause it to outright shut itself off sometimes...

 

Relay is likely integrated into the TIPM..... (which I thought was just a stupid idea..... one 4 dollar part fails, and you have to replace the 1000 dollar assembly???? Where in the world does that make any sense?) It may be getting weak. I know there was an issue with fuel pump relays on some trucks, and the aftermarket came up with a 'repair kit' for that, wonder if there isn't something similar for the a/c.

If you are losing power at the compressor, that would certainly disengage the clutch. Need to find out WHY you are losing power. Low pressure might do it, but, that would normally just cause the compressor to short cycle..... I think the circuits the PCM uses to decide if it wants to activate the relay, are completely separate from pretty much everything else..... Think I might test and see if when the compressor quits, is the PCM still commanding it on? (relatively high zoot scanner required I would think....)

 

I'm not surprised the relay would be built into the TIPM, but that makes this quite a bit more complicated. Do you think a failing TIPM would explain the harness recieving power again if I jump the compressor with 12 volts??

Honestly I think the pressures are fine, it's as happy as a clam when it's running. Just suddenly the compressor quits recieving power sometimes, confirmed when using a test light on the plug... I've jiggled the wires around the harness and did a basic visual inspection but all of the factory looms are in pretty honestly impressive shape, nothing looks out of the ordinary, no cuts or dirt built up in the harness... Do you know/have a diagram where I can probe with a test light/multimeter to see if the PCM is still commanding power on, and maybe what color wire I should be on the lookout for? The compressor plug always has a perfect full time ground, so I think it's definitely a power feeding issue, and not a ground issue. Thanks for the help.

 

Trouble is, there are a selection of reasons the PCM would decide to turn off the compressor..... bad pressure switch, if there is a temp sensor on the evaporator core, that could cause it, and heaven only knows what other reasoning dodge has under the hood there. Would need a service manual to go thru, to see how the system is 'supposed' to work.... As I said, I suspect a fairly high zoot scanner is going to be required for complete troubleshooting.

 

I'll probably need a good factory service manual then, I doubt a Haynes will have the information I'll need.

I have a scan tool I think I might be able to use. Is there really a temperature sensor on the heater core? I figured with the AC set to max the temp sensor wouldn't shut down the compressor...

Hopefully I can pick up a good factory service manual without spending a small fortune.

 

There might be a temp sensor on the evaporator core, and if it gets below a certain threshold for an amount of time, PCM may shut down the compressor. I don't know if yours actually works that way though. And yes, a factory service manual is going to be a requirement. Haynes/Chiltons are pretty generic. Service manual is specific, and has information that is actually accurate.

Plug your scanner in, see what interesting data it is willing to hand you.

 

I scanned the computer, wiped the codes (a few were set when I was servicing the AC), and ran the truck and AC and it worked for a second and then cut off. And this code was set, a P0533. Pressure sensor "A" circuit high.. what does this mean? Could this be the source of my issue?

 

Just drove it around for a short while, it's working most of the time, it cuts off for a bit and gets a bit warm (still relatively cold) before coming back on. Although it's late and cool right now, I'll drive it again in the middle of the day and see how it behaves, that's usually when it acted up.

 

" The electric fan works when the clutch is running, but it shuts off when the clutch stops . . "

Not a mech or AC expert by any means, but is this statement backwards? I.e., might the compressor clutch running depend on whether the condenser fan is operating properly? Here's why I ask:

I had a somewhat similar issue with my '07 5.7L. The A/C would work fine when the vehicle was in motion, and RPMs were above idle; but when at idle (e.g., at a stoplight), the compressor would cycle on and off, with warm air blowing when off, of course. Refrigerant charge was OK, and I replaced the pressure sensor & compressor clutch/coil without success.

Turns out, the condenser fan was inop. I was getting ready to replace it, but for grins, I rapped the back of the condenser fan motor with a hammer, and it started working. As soon as the fan came on, the AC clutch engaged (which is why I made the statement in the 1st line), and everything was fine.

Yours might be a completely different issue, but I thought I'd throw this out.

Good luck.