Mercury Repair Questions? Ask a Mechanic for Answers ASAP
Hello I can help,
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Can you tell me what is the model, year and engine size your Mercury is?
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?
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
Off unless you have a vacuum gauge?
Have you pulled the vacuum reservoir from the wheelwell as shown in the procedure I posted above?
Do you have a vacuum gauge?
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.