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!
  • Home
  • Questions
  • 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: AC air coming out defrost channel

This is an indication that the mode door actuator within your dash has gone bad. This actuator is responsible for moving the door that allows or blocks off air flow to a certain vent location. Sometimes this part can be...

Q: I'm trying to find out if I can run tbi without a computer

You cannot run the injectors correctly without a computer to operate them. You cannot just open the injectors and run it that way since it would get too much fuel.

Q: Thinking of buying a car owner said it needs a freeze plug how much would that be on a 2000 Toyota Camry

Hi there - unfortunately, replacing freeze plugs is not a service YourMechanic.com offers at this time. I do recommend a Pre-Purchase Inspection performed by a mobile, professional mechanic, such as one from YourMechanic, who will come to the vehicle location,...

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...
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...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...