A/C warm at idle

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Jimmy9190

Jimmy9190

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Feb 17, 2007
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Clermont, Florida
This is about the 2001 Dodge Dakota in my signature. I did search but did not find much info on this problem. A couple of days ago I noticed my AC was blowing warmer air when I was sitting at a red light and would get noticeably cooler once I got moving down the road again. I do have a low side gauge from one of those DIY recharge kits, it showed about 50 yesterday when I checked it and the temp outside was about 75. I know that type of gauge is not the best way to test but it was all I have on hand here at home. My e-fan in back of the condenser is turning as soon as I turn on the AC. My engine is not overheating so I don't think the fan clutch is bad. It should not be bad, it is a genuine OEM Mopar fan clutch, I think I paid $120.00 for it in the summer of 2010, about maybe 30,000 miles ago.

Any ideas or anyone here had this problem? If so what was the fix? Compressor getting weak? I replaced the compressor about 5 years ago with a new Napa compressor. My OE compressor was working fine but had a bit of a growling noise so I replaced it as a preventative measure. I had the refrigerant evacuated and recharged after I was in an accident in March 2010. I don't see any evidence of a refrigerant leak but that does not mean a leak does not exist. My AC clutch is engaging and spinning but tonight I seemed to be hearing a funny warbling noise when I had the AC on and doing about 45 mph. The noise disappeared when I turned the AC off.

I am going to check the whole system as best as I can this weekend, may even splurge on a cheap set of AC gauges. Thanks for any help with this.
 
Get some real gauges and see what's really going on. Static pressure readings on a fully cold vehicle can inform you if there is any liquid content still in there, and then operating pressures can tune you in. Best of course is a full vacuum to less than 500 micron for a while and then refill by mass.
 
I think your problem has two possible causes: condenser or compressor.

If, standing still, you raise the engine rpm to 2500 rpm and you get cold air, then the problem lies in the compressor, could be the clutch pulley, the auxiliary belt or the belt tensioner. If they are OK then the compressor itself could be worn out.

On the other hand, if raising the engine speed you get warm air, and you only get cold air when you are moving, this would indicate a problem in the cooling of the condenser, something is blocking air flow to it or the fan is not moving sufficient air because of a broken blade or is not spinning fast enough because of a shorted winding.

P.S. The fact that you get cold air leads me to believe that the refrigerant gas is not the source of the problem.
 
The symptoms as described are all about air flow over the condenser. Fan, clutch, bugs/debris, etc.

AC compressors work well at idle IF the condenser is cooled.
 
Thanks for the info. I don't usually need the ac in the morning this time of year but it blew ice cold coming to work today. It was only about maybe 68 degrees outside though. I did not hear the odd warbling noise either. I will try the ac on my way home, it should be close to 90 this afternoon. I will rev the engine at idle and see what happens. My condenser looks clean to me but will take a water hose to it and clean it out anyway. Can pollen get in a condenser and cause this problem? I have a tree right next to my driveway that is putting out real bad thick pollen right now. And how can you tell if the condenser fan is not spinning fast enough?

Thanks again for helping me on this.
 
Darwin nailed it. Rev it up sitting still.if it cools its the compressor. If it starts cycling and not cooling its air flow. Just cause the fan clutch is new and from the dealer does not guarantee it works.
 
Good advice already given. My bet is on the compressor having "lost" a cylinder or two- usually due to reed valves failing and not actually a heavy mechanical problem- when swash-plate compressors actually have a big failure, they lock up solid. But given that they usually have between 5 and 7 pistons, each with its own set of reed valves, its pretty common for reed valves to start failing and the owner not really notice much until more than one or two cylinders are affected. Then it gets just like you describe- no cooling at low RPM, the high side pressure goes down, and the low side pressure goes UP. The compressor actually serves as a vacuum pump for the low side, and when it loses capacity the low side pressure goes higher than normal.
 
I had the same warm AC at idle coming home today. While sitting still I revved it to 1500 for a minute, AC became markedly cooler. I checked the fan clutch, it appears to be OK, only moves a couple inches when I give it a good shove with my hand, still feels nice and firm. The fan clutch also still engages for the first 1/8th of a mile each morning when the truck is cold and I am headed off to work so I believe it is OK. I can almost smell a burning odor around the compressor when the engine is running and AC is on. That may be just heat from the engine but I never noticed it before now.

I checked my file of parts receipts and the Napa compressor I put on back in 2008 only had a 2 year warranty, long expired now. It was also a reman, I could have sworn I bought new but the receipt says reman. So I will try to check it further tomorrow but it looks like I need a new compressor. I think if it were low on R34 it would blow warm air all the time. When driving it it cool but not as cold as it was just last week. Up until now I have had no AC problems at all since 2008. Thanks for the help and ideas here.
 
^+1. I have installed remanufactured for others - their choice. Three year life span, tops.
 
How about a used OEM Denso compressor from the junk yard? I can get one there for $75.00. I have heard used OE is better than new aftermarket..

Thanks for your help on this.
 
Originally Posted By: Jimmy9190
How about a used OEM Denso compressor from the junk yard? I can get one there for $75.00. I have heard used OE is better than new aftermarket..

Thanks for your help on this.



That is what I have always done. Never had to put a second on either of the two cars that I put boneyard A/C compressors on.
 
Partial update here...fan clutch is shot. You can stop the fan from spinning while the truck is idling just by touching the blades with a screwdriver handle. Compressor is shot. I took half a day off work today, took my truck to a shop, they first found the freon was low so they evacuated and recharged the freon, temp at the vent only went as low as 70 and that was with the tach at about 2,000 RPM. The fixed orifice tube had some small metal fragments in it, put in a new one but the AC still would not cool below 70 unless you held the throttle down. Shop estimate to fix it with new compressor, new fan clutch, new receiver-dryer and re-charging the freon was right at $1,200.00..

So I had the shop evacuate the system and not re-charge it. Shop charged me $100.00 for diagnosis time and a new orifice tube, which I think is more than fair. I will buy my own parts and replace the compressor, drier and fan clutch myself and then have the shop re-charge the freon later this week. As it stands now it will cost me about $500.00 in total parts and labor, just figuring it without a calculator handy. If I buy a used OEM Mopar compressor from the junk yard it would save me $140.00. I may do that and use new for the rest of the parts.

Gotta fix it soon, as it is now I have no AC at all. Luckily we have a cool front and maybe some rain coming tomorrow.
 
Often you can buy a brand new compressor that was not the same as OE, and was made in China every time. They have a similar price to cheap rebuilds that are carelessly sprayed with cheap black paint.

That in mind, I don't know how long they last. They do last long enough to meet the repair shops's warranty period.

Some of my mom's cars had such problematic compressors, that they might as well have been cheap rebuilds.
 
I second the motion to purchase a junk yard compressor...I went through several Four Seasons compressors for our Jeep (each time thoroughly cleaning the condensor and replacing the orifice (made into the line) and each failed within a month. Installed a junk yard compressor with the matching orifice line and it's been working great ever since.

The only other issue was cheap, leaking cycling switches from AA. The original switch was re-installed and working fine.
 
How about a condenser from the junk yard too? From what I am learning the debris from the compressor winds up in the condenser. Rather than trying to flush the condenser why not just use a good used one? The junk yard has a 90 day warranty on their parts and it would save me more money.

Also is it really necessary to buy the flush kit and go to all the trouble to flush the evaporator and the lines or was what I read about the debris collecting in the condenser really true? My truck has a fixed orifice tube which is also said to collect the bulk of debris. Can I just flush the lines with air, replace the condenser, drier and compressor, recharge it and be OK?

Thanks for any info and help on this. I do not know much about AC but am trying to learn what I need to do before I get started on it.
 
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