Skip the auto shop - Our mechanics make house calls

Q: Air conditioning works, but during longer trips it becomes weaker and weaker.

asked by on

On longer trips, the air conditioning will begin to not keep the car cool, and I'll need to turn the fan higher and higher until I'm at max A/C. Once max A/C will no longer keep the car cool, I'll turn the A/C off, roll down the windows, and after a while, the A/C will be "recharged" and will again begin to push out cool air. Any idea what the problem is? Thanks!
My car has an automatic transmission.

A: First thing to do is check the refrigerant ...

First thing to do is check the refrigerant charge level, typically via gauge (high and low) pressures, although note that gauge pressures do not perfectly coincide with what is intended to be the factory specified amount of charge (measured very precisely in ounces, indeed tenths of an ounce) of R134a.

Gauge pressures will tell you if the system is clearly low, as well as give you an overall indication of the function of compressor (e.g. the compressor is "compressing"). If charge is good (e.g. if pressures are within acceptable range and STABLE), you want to check and make sure the condenser is not blocked with debris or has lots of bent fins. You want to be sure that the condenser fan works, as well as radiator fan, which also draws air over condenser.

Intermittent cooling can sometimes be caused by excess moisture in the system. The moisture can freeze in the expansion valve blocking flow of refrigerant. If your system has not been opened though, there is no reason for moisture to have gotten in except in a circumstance where refrigerant level in your system has gotten so low that the low side has drawn a vacuum and air has leaked in. At any rate, check gauge pressures first. If you would like to have this checked, a certified professional from YourMechanic can come to your car's location to inspect the AC and let you know what needs to be done.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%

Get a quote

What others are asking

Q: Abs, brake, and vsc warning lights

Hello. Most of the time if the vehicle is running fine and the lights just came on then you more than likely have low brake fluid. If the fluid level is low then all of these lights will come on....

Q: Cheap sports car

The Miata is a good choice. They are fun to drive, there are many clubs for them and performance upgrades are readily available. Their small size makes them easy to work on; they are quite simple. The Eclipse is...

Q: Truck runs fine once jumped until turned off

Hi. Generally, a charging system problem will illuminate the battery light in the instrument cluster and the engine will quit as soon as the battery is discharged. With that being said, the problem either lies in the battery itself, or...

Related articles

P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...