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Ask George H. Your Own Question
George H.
George H., ASE Certified Technician
Category: Mercury
Satisfied Customers: 18489
Experience:  ASE Master 15+ years
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Ron, my ac works just fine, the problem is when I accelerate

Customer Question

Hey Ron, my ac works just fine, the problem is when I accelerate the ac/air switches from face to my feet or to the defrost vent and it just keeps doing that as I drive my grand marquis... Please help me
Submitted: 7 months ago.
Category: Mercury
Expert:  George H. replied 7 months ago.

Hello I can help,

Looks like Ron is not online now,

Can you tell me what is the model, year and engine size your Mercury is?

Customer: replied 7 months ago.
Mercury grand marquis 2001 4.3
Expert:  George H. replied 7 months ago.

Great, can you find the vacuum hose going through the firewall on the engine side near the heater and AC lines in front of where the passenger sits?

Customer: replied 7 months ago.
I have they're in my hand
Expert:  George H. replied 7 months ago.

Ok, make sure you have no leaks there and in the left fenderwell under the relay box is the vacuum reservoir. Check it for leaks

Click here for procedure

The vacuum system reservoir is leaking, check the hoses and lines and it should be found on visual inspection. Just follow the hose

Customer: replied 7 months ago.
Should the vehicle be running or off while checking for this ?
Expert:  George H. replied 7 months ago.

Off unless you have a vacuum gauge?

Customer: replied 7 months ago.
There is no leak I've check it vacuum hose ?
Expert:  George H. replied 7 months ago.

Have you pulled the vacuum reservoir from the wheelwell as shown in the procedure I posted above?

Do you have a vacuum gauge?

Customer: replied 7 months ago.
How can check the vacuum reservoir for leaks it's an empty box I can't get it open ?
Customer: replied 7 months ago.
I have taken it off the reservoir and no I don't have a vacuum gauge
Expert:  George H. replied 7 months ago.

You don't need to get it open just put a clean hose on it and suck to see if it leaks.

I think Autozone has a vacuum hand pump in their loan a tool set. If you can get that you block the inlet to the system at the vacuum tree on the top of the firewall and pump it up. If it does not hold then you plug parts to see what stops the leak like going down a tree.

I would plug anything to the reservoir first and into the cabin of the car. If no leaks you need to test the reservoir then the interior. Sometimes the control head leaks but usually not enough for the mode doors to change position. That is usually the reservoir.