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.

Hi, thanks for writing in. I suggest checking the AC pressures to see if the refrigerant 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 [https://www.yourmechanic.com/services/ac-is-not-working-inspection), 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!
  1. Home
  2. Questions
  3. I have a 2000 Mercury Mountaineer and the AC only works if I'm going under 40-50mph

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: A/C problem

There are innumerable things that can go wrong with the A/C system and so the best thing to do is request an air conditioning system inspection and the responding certified mechanic will get this resolved for you. The possibilities that...

Q: Car won't shift into any gear once warmerd up.

Considering the age and low mileage of your 1986 Chevrolet Camaro, two simple things may help your situation. Change the transmission fluid which 1986 is one of the odd years that GM specifies automatic transmission fluid rather than gear...

Q: 2000 Ford Explorer. Check engine light is on. Issues with the heat. Replaced fan blower. Now no air coming out of vents or defrost

Hello, thank you for writing in. Unfortunately, without knowing what engine code has triggered it is difficult to say what the issues may be or if they are related. Bank 2 refers to one side of the engine, and there...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...