A/C compressor "pulsing" and nearly stalling my engine at idle

I just turned over 150k on a 2004 Dodge Ram 1500, and this weekend, it started to take a while for the A/C to cool. It would not cool if I was idling. But it would cool just fine when driving.

Today, I was using the truck to pull stumps, and while letting it idle, I noticed that the a/c compressor is cycling about 5-6 times per minute, and causing the idle rpms to dip a bit. More than usual.

The a/c was not cooling due to it idling, and i put the gauge on it and it was WAY up in the red (on the low pressure side).

Then I let some of the freon leak out into a welding glove, and it was oily, but not cool. Tubes are body temperature also.

I am assuming compressor is shot.

How much can I do at home, or should I just let the shop do it all?

I have done my mom's Xterra, and we swapped the compressor and dryer, then let the shop fill it and pressure test it, and it saved us a bunch of money. Can I still do this with a newer car?

 

I would try and throw a can of 134a in it first. What PSI is the "red" part of your low side gauge? Sounds like it's just low. It will read high on your low side gauge because of the cycling.

 

What is way up in the red....Does it give you a pressure reading??
If the compressor is not running, the low side pressure will be high (since nothing is pumping the refrigerant) If the compressor is cycling, then it could be low on refrigerant...Have you ever had anything done to the system before??

 

I bet it's the condensor fan causing it. I have gone thru 2 of them, same symptoms.

 

OK, then it is probably low.

It is the stock system, all I have ever done is add a can of freon early last summer. It probably has a slow leak, and just now that it is warming up it is noticeable.

It still cools VERY well, and we just drove home from dinner and I had to turn it down. So I was thinking the compressor is working too well to be "broken".

But if the pressure is high when the compressor is not on, then that is my problem. At idle, it comes on for just a second or 2 then turns off for about 6-10 secs, then comes on for another second.

So when I checked the pressure, the compressor was off.

 

So, just to clarify, when the compressor goes off, the entire system sorta goes into equilibrium, making the low side higher and the high side lower?

If so, that makes complete sense.

 

Trust me on this one. Turn on the AC. The fan should come on in about three seconds. If it is not on then tap on the butt of it and see if it tries to spin..

 

It will somewhat equalize. But temperature will effect the pressures. You could also have a restriction in the system, of it might be over charged. Those cans are a bad idea, it's a balanced amount of refrigerant that does the work, so it's easy to mess it up. Don't ever use the sealer stuff!!
I was amazed at the refrigerant you can buy in the parts stores in the USA..up here it's a restricted chemical, with the whole green house and cancer thingy...

 

When the system is off it equalizes pressure between high and low lines. So your reading will be "in the red" on the low side when the system isnt operating.


It sounds like its either hitting a low pressure switch or high pressure switch. Could be low freon, a bad switch (either), or could be numerous other things.

I would see what it says with a set of gauges and running to better diagnose without guessing.

 

If you find that it is the fan, I have a few tricks to get it out.

 

Well, 9pm and checked it and it is all working 100% AOK. and pressure is in the lower half of the blue range, or right where it should be. But it is only 69 out there, and not 80 like earlier.

I will keep an eye on that fan, as Gene stated. I will have to wait til tomorrow afternoon and watch it.

 

When the fan isn't cooling, the pressures almost equal out when reading guages. I like the fact that nothing goes out when the fan malfunctions. I have seen hoses blow and compressors/clutches crap out etc on other systems.

 

Gene, does the compressor cut out when the fan stops? Becuase I can clearly see the compressor only coming on for a second, then going back off for 5-10 seconds, and trying again.

I will check it today in the middle of the hot day and see what is going on.

 

No. The compressor comes on and stays on unless the low side gets too low or the high side gets too high.

 

Still keeping an eye on it, and hearing from various places that if the pressure is even a little low due to low freon, it will flip switches on either the high pressure end, low pressure end, or at the fan.

So I added 3/4 can freon and it seems to be working well. No cycling at all, but the real test will be when it gets hot later today.

For what it is worth, the pressure is right in the middle of the blue area on my gauge, which is 35 psi. While it was going in, I hit the vent with my infrared thermometer and watched it go from 54 degrees down at one point to 28.5!!! Now THAT is COLD!!!