CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

AC Works only when engine is revving high

1998 Honda CRV

Replaced the AC compressor. AC is cold only when the engine is revving above certain rpm. When at a stop, the air is warm…but if I put it into neutral and rev the engine to, let’s say, 2000+ rpm, AC gets colder…or when Im driving, obviously.

I know everyone is gonna say something about the condensor fan but would it be the fan given above circumstances?

Did you vacuum down the system before charging the refrigerant?

I didn’t do anything - a mechanic did the work.

Then your CRV needs to go back to the mechanic or better yet…an independent AC shop.

lol…I understand that. Im trying to diagnose the problem myself…just for my own info. Telling me to take it to the mechanic doesnt answer my question. Thanks tho…Good advice.

The system is probably low on refrigerant. But not low enough to prevent the low pressure switch from preventing the compressor from operating.

If you want to try to fix this yourself, go purchase a DYI AC recharge kit.

Once the recharging kit is connected, start the engine and raise the idle speed to 2,000 RPM’s and turn the AC on. It would be ideal if there was a large fan blowing on the condenser at the front of the vehicle.

Now add refrigerant to the system until the temperature out of the vents is constant and the gauge stays in the green zone under all RPM’s.

Tester

1 Like

I mean…I just had the mechanic replace the compressor for $800. He said everything was good to go. I would think that he “filled the refrigerant to the top”. I guess you never know. I’ll have it checked out. It seemed to me like the condenser is not getting cooled when not moving…which leads me to believe it has something to do with the condenser fan. But Im confused by why air would cool when I rev the engine in neutral without the car moving.

Here is some more info: I parked the car and ran the AC. The air is warm when idling at 800rpm. When I rev the engine to 2000+, the air gets colder. This is definite. I thought maybe the condenser fan was not running when just idling - so I opened the hood to look at the 2 fans attached to the radiator while idling. Both fans were running. And the AC air was warm.

Does this give you any other hints?

I would need both high and low side pressure readings at idle and at 2500rpm to hazard any guesses.

can you give me different scenarios?

Well, no, not really. There is so much information that gain be gained by watching gauges, their relation to each other, and knowing engine speed, ambient temperature, discharge temps, and temperatures throughout the system that it’s not easy to relate them all in a paragraph or two.

Is the compressor engaging at idle?

1 Like

Dont know. All I know is what ive stated above. I know the air is warm, I know both fans are running. I know air gets cooler when I rev the engine. How can i test/check to see if the compressor is engaging at idle?

Turn on the A/C with the engine idling and look at the outer face of the compressor, the part forward of the belt, if you will. That should be turning along with the belt.

Yup…everything is turning when the AC gets turned on at idle. Also, both fans start to turn when i turn the AC on at idle.

Still low on Refrigerant. Return to the shop for the mechanic to top it off.
Or there is a O-ring that didn’t seal properly and the refrigerant leaked out.

Yosemite

Then one of two things is the problem.

Either the system is low on refrigerant, or there’s a problem with the expansion valve.

Tester

I agree that both high and low side pressures need to be known before even a reasonably close guess could be made as to the problem.

Offhand it sounds like a low refrigerant charge. If that’s the case and the mechanic did fill the system with the correct amount of refrigerant then the system needs to be leak checked.
This should be done after any A/C repair. Whether this was done on your car I have no idea.

Hello there
I’m having the same issue but my AC specialist told me that my AC compressor is weak so it’s not circulating the AC fluid properly… so I would recommend you let your AC specialist check if you have a good circulation even though it’s a new compressor your using.

I think since this thread is 4 years old they may have solved their problem by now.

I’m having the same problem with my 2008 honda civic. Did you ever find out what the problem was? thank you very much for your help!