Possible a/c issue

[SHobbs]

In my 04 while using the a/c when I pull up to a redlight or stop sign the RPM's bounce when I lift my foot off the go pedal. It bounces a couple time before settling on the normal speed. Yesterday, I started the truck and it acted like a dead miss at idle, like an injector was was dead. When I turned off the a/c the idle returned to normal and drove normal no issue at all. Turn on the a/c and it idled rough again.

 

[Tuesdak]

This has fuel system written all over it. FPA on the CP3 for RPM bounce. Dead miss feel on my 2003 was an injector that quit firing combined with high return rate on another. So you may just have high return rates where the ECM can’t control the pressure anymore.

A/C in this case is likely just a load showing fuel system unable to cope.

 

[SHobbs]

Been told that the a/c compressor could be getting ready to go, locking up. The day before all this I drove the truck about 750 miles, no issues at all. It was the next morning it started acting up and the odd thing about it is once I turn off the a/c everything runs normal

 

[Tuesdak]

Suggest pull the engine fan belt and inspect it and all pulleys for rough bearings. Inspect the compressor clutch for a broken drive spring. (Engine vibration that feels like a miss.)

Is the compressor making any noise? I assume the A/C is cooling properly now? If it really is a compressor locking up you will know real soon. But I doubt it. This engine will easily burn the belt clean off the engine and not exactly notice a locked up A/C compressor.

A quick check if it's load alone on the engine causing a problem is to take it out of gear at a stop to reduce load when it's acting up with the A/C on. (Assuming AT)

 

[SHobbs]

The compressor is quiet when all this is going on. I don't have the truck at the house currently, planning on picking it up later this week, getting this figured out would be nice it's too hot in Texas to drive without a/c. As I said everything on the drive here there were no issues, truck ran perfect, rpm bounce was at stop signs and red lights when I push the clutch in and lift off the go pedal and only with the a/c running.

 

[Claude15]

I had similar symptoms with my 2007 manual transmission. Driving at low rpm with the ac on, (across a parking lot) the motor would stumble in a cycle.
It ended up being the ac compressor clutch. The bad clutch also produced many random codes. I replaced the compressor, deleted the codes and all is well.

 

[Mike Wenrich]

I just changed a compressor on a 2003 RAM hemi for the same reason. The engine was off and on slowing down. But in this case the compressor was making noise as it slowed down...locking up. Still blowing cold air at the time.

 

[SHobbs]

Finally got the truck to the house. Running the rpm's to 1500 turn on the a/c and the rpm's slow to below 1000, turn it off and things return to normal. Now, when taking off in any gear the engine has a huffing sound, best way to describe it is like the blades of a Huey beating the air. It definitely has a shimmy to it when taking off combined with the sound. I need to remove the belt and see if there is anything causing it like the a/c compressor or I may be looking into the fuel system as to a cause. Here I was bragging on the darn thing when I drove it the 780 miles to get it here, with worn out original front control arms, worn out tie rods and who knows on the track bar it never death wobbled, rode better with better road manners than my 2013 and the a/c worked. It still works and is cold but something is going on.

 

[Mike Wenrich]

Hard to imagine it's anything but the compressor. Taking the belt off is going to be the same as turning the switch off. You won't have the compressor in the diagnosis. If it's okay with the A/C off then one would think that is the problem. You might start first having someone engage the A/C while you have your head under the hood. the compressor should be making noise if it's a bearing, which was the case with the 03.