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.

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!
  1. Home
  2. Questions
  3. Air conditioning works, but during longer trips it becomes weaker and weaker.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Power steering pump whining and leaking

Hello. If the system is losing fluid then there must be a leak somewhere. Most of the time the leak is at the rack and pinion so it tends to leak further back on the vehicle. If the pump only...

Q: Coilovers and Sway Bars 2002 Lexus IS300

Hi there - upgrading your suspension with coilovers and sway bars is not terribly difficult, and is largely an "unbolt the old, bolt on the new", followed by an alignment. It does, however, require appropriate equipment to raise and safely...

Q: Check Engine light coming on

The P0440 code is for a malfunction in the evaporative emissions system. This is a control system malfunction code so there may be a component the vehicle computer is trying to activate that is not functioning properly or there may...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.