AC works under 1.5k rpm

DarthHemi · Jun 25, 2022

2004 1500 SLT quad cab long bed 5.7

When parked and idle the AC clutch will sometimes kick on and then just stop

While in gear, if I slow down in traffic and rpm drops below ~1.5 the AC will work, the clutch kicks on

While in gear and above ~1.5k rpm the clutch will disengage and not run

Vehicle has ~350k miles and the AC Compressor looks original. Im considering just replacing it the compressor with one from Rock Auto. Which one does everyone recommend?

2004 DODGE RAM 1500 PICKUP 5.7L V8 A/C Compressor | RockAuto

RockAuto ships auto parts and body parts from over 300 manufacturers to customers' doors worldwide, all at warehouse prices. Easy to use parts catalog.

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If it may be something else, Im happy to diagnose.

Thanks!

DarthHemi · Jun 25, 2022

Clutch coil is returning 4.2 ohms which is good

pacofortacos · Jun 25, 2022

You have to check to see if it is electrical or mechanical.
Test for voltage at the coil and see if you have 12 volts and ground there when the clutch is not engaged.

If you have voltage and no clutch engagement then it is the compressor clutch.
If you don't have voltage then it is elsewhere.

DarthHemi · Jun 25, 2022

Followed this procedure and it passed: https://www.youtube.com/watch?v=k8IQnkqvXIQ&t=11s

PoMansRam · Jun 25, 2022

As a blind guess the pressure switch may be commanding the compressor to cut off as pressure builds at higher RPM. Could be low on refrigerant, could be a faulty press switch, the condenser could be plugged, etc...etc..

chopperman1 · Jun 25, 2022

You don't mention checking pressures. Could simply be a leak and low on charge. I'd certainly be checking that before replacing a compressor.

pacofortacos · Jun 25, 2022

chopperman1 said:
You don't mention checking pressures. Could simply be a leak and low on charge. I'd certainly be checking that before replacing a compressor.

If you don't have a set of gauges, you might be able to get away with checking the low side pretty cheaply using the stuff the guy in this video does.

I can't believe Mechanics don't know How to Recharge AC system correctly!

The Number 1 cause of Car AC not working is such a easy fix. Some mistakes are so simple example performing the Recharge in the shade.Arctic freeze auto AC R...

www.youtube.com

Oliver Closehauf · Jun 26, 2022

I was going to do all of that myself and try to save some money, but in the end I said just let a trustworthy shop do it. Comes with a warranty and I don't have to mess with it. I'll do anything if I have the right tools, but those AC tools are tools I don't have.

DarthHemi · Jun 26, 2022

So I checked the relays. I switched fuel pump and AC clutch, no change. I replaced the AC Fan control and it worked for like 20 minutes and stopped working.

I checked Low pressure line and was at 100 psi. Rechecked power and no voltage to compressor.

What can cause no voltage to compressor?

Thanks

DarthHemi · Jun 26, 2022

If i jump 12v everything seems to work fine. Does that mean a AC pressure sensor?

DarthHemi · Jun 26, 2022

This is my target: https://www.oreillyauto.com/detail/...004-dodge-ram-1500?q=AC+Pressure+Sensor&pos=0

Is there an installation procedure? Haynes is kinda weird

jws123 · Jun 26, 2022

DarthHemi said:
So I checked the relays. I switched fuel pump and AC clutch, no change. I replaced the AC Fan control and it worked for like 20 minutes and stopped working.

I checked Low pressure line and was at 100 psi. Rechecked power and no voltage to compressor.

What can cause no voltage to compressor?

Thanks

If it was 100 PSI when compressor is running then it has to much. It needs to be checked with ac compressor running bet your low on refrigerant.

jws123 · Jun 26, 2022

DarthHemi said:
This is my target: https://www.oreillyauto.com/detail/...004-dodge-ram-1500?q=AC+Pressure+Sensor&pos=0

Is there an installation procedure? Haynes is kinda weird

To replace this you recover/De charge system change it and then evacuate/re charge system.

Oliver Closehauf · Jun 26, 2022

What's the low side pressure with the compressor running? Maybe watch that gauge for 20 minutes and see what happens to the pressure when it kicks off.

pacofortacos · Jun 27, 2022

If your low side is @ 100 psi WITH the compressor running, it might be a bad orfice tube, plugged receiver drier, or really over charged. The pressure switch is most likely turning off the AC because of a pressure problem.

They used to have expansion valves years ago, but I think yours uses an orfice tube. I don't know if the tube is before or after the drier.

More Information for UAC EX4101C

crash68 · Jun 27, 2022

pacofortacos said:
I don't know if the tube is before or after the drier.

an orfice tube (or any expansion device) will be after the receiver/drier in a refrigeration system.

DarthHemi · Jun 27, 2022

If I give 12v straight to the compressor why does it work?

I read high side under load is over 200 psi. When both sides are 100 (I didn’t check high) it means the compressor isn’t running and not getting voltage.

DarthHemi · Jun 27, 2022

So its working, for now, in my driveway.

TLDR - Replaced AC Fan relay, then AC temperature switch, then AC clutch 10a fuse.
TLDR 2 - check your fuses first to make sure

Full story:
It was running yesterday after replacing the AC Fan relay. Then driving down the road it just stopped. I troubleshot the issue. and noticed no power coming to compressor. As part of this troubleshooting I was connecting leads to the wiring harness and compressor. Im speculating here I did something to blow a fuse.

Replaced the AC temperature switch this morning. Nothing worked. Checked AC Clutch fuse and it was blown. It would have been nice if I would have checked the fuse prior to replacing the switch (I guess I could put the old one back). Replaced fuse. It is running properly in my driveway.

Checked low side AC, was at ~30psi. Brought it up to ~40 with some additional r134a. All seems well.

Since Im a betting man, my speculation is that after another 10-15 min of driving im going to blow another fuse. If that happens signs are pointing to a rusted/semi-seized clutch which would indicate a compressor replacement, no?

Thanks again all for the help

pacofortacos · Jun 27, 2022

crash68 said:
an orfice tube (or any expansion device) will be after the receiver/drier in a refrigeration system.

I know the expansion valves were, but I couldn't see where it went in a diagram and wanted to not give information that I was unsure of.
I thought they were usually always right at the evaporator inlet.

pacofortacos · Jun 27, 2022

DarthHemi said:
So its working, for now, in my driveway.

TLDR - Replaced AC Fan relay, then AC temperature switch, then AC clutch 10a fuse.
TLDR 2 - check your fuses first to make sure

Full story:
It was running yesterday after replacing the AC Fan relay. Then driving down the road it just stopped. I troubleshot the issue. and noticed no power coming to compressor. As part of this troubleshooting I was connecting leads to the wiring harness and compressor. Im speculating here I did something to blow a fuse.

Replaced the AC temperature switch this morning. Nothing worked. Checked AC Clutch fuse and it was blown. It would have been nice if I would have checked the fuse prior to replacing the switch (I guess I could put the old one back). Replaced fuse. It is running properly in my driveway.

Checked low side AC, was at ~30psi. Brought it up to ~40 with some additional r134a. All seems well.

Since Im a betting man, my speculation is that after another 10-15 min of driving im going to blow another fuse. If that happens signs are pointing to a rusted/semi-seized clutch which would indicate a compressor replacement, no?

Thanks again all for the help

Most likely, you could unplug the clutch and drive it a few days (with the AC on - though not working) and see if it blows the fuse and if it does, that would indicate a short elsewhere. If it doesn't then it is most likely the coil and since they really don't sell the clutch/coil as much as they used to ( I used to replace those often years ago) you would need a compressor.

AC works under 1.5k rpm

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