Skip the auto shop - Our mechanics make house calls

Q: I have a 2000 Mercury Mountaineer and the AC only works if I'm going under 40-50mph

asked by on

The AC works great but only when I'm driving below 40ish mph, if I'm on the highway it blows really warm and the heater only blows cold air.

My car has 150000 miles.
My car has an automatic transmission.

A: Hi, thanks for writing in. I suggest checki...

Hi, thanks for writing in. I suggest checking the AC pressures to see if the Freon is full and check if the compressor cycles in and out at the proper pressures. The low pressure side should cycle out at about 24 psi. If the low side gets below that, then your evaporator may freeze causing no air flow through it and will blow warm or if the compressor cycles out and not back in at high speeds. The pressure cycling switch may be bad. If you would like help, consider having an expert automotive technician from YourMechanic come to your home or office to [, and make or suggest any repairs as needed.

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: How do you use the heater and air conditioner?

Depending on the trim level of your car, you have either a manual heater and air conditioner or an automatic climate control system. If your system is manual, here’s how to use it: Heat: To turn on the heat,...

Q: Car potentially vapor locking, not starting.

Hello, I would doubt that you have a vapor lock problem. A vapor lock problem usually only occurs when temperatures get hot enough to make the fuel near the pump vaporize. This is not your problem because the car is...

Q: Antifreeze emptying out fast

Hello. If this happened right after the work was done, then it is typically caused by a hose that is loose or the thermostat not being installed right. If you cannot see the leak, then the system will need to...

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...
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...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.