I have a 1999 Lincoln Towncar V8. I bought the car used and have had a particular issue from that time, that I want to know if it is normal, or if it is correctable. When the A/C is running, I notice that it "goes away" a lot when I accelerate the car. When I accelerate, the fan is still running and air blowing out, but the blowing power seems to decrease, and the little bit of air still coming out as I accelerate is not as cold. It blows full and cold as soon as I let off the accelerator. Is this indicative of a problem? Vacuum issue maybe?
The A/C runs fine otherwise.
FYI- I've only owned one other Ford product in my lifetime, (87 Grand Marquis) and it did the same thing.
Appreciate any help.
Yes, I would be looking for a vacuum leak.
Intake manifold vacuum is at it's highest at idle, and decreases with engine speed and load. The majority of the A/C air control system is powered by vacuum.
There is most likely a leak in the main vacuum line which goes through the firewall and feeds the system. The line will start somewhere on the intake manifold, go to the vacuum reservoir which appears to be located in the left rear corner of the engine compartment (possibly under the cowl), and then through the firewall and to the system.
Follow the lines looking for cracks, breaks, kinks, burns, etc. A cracked vacuum reservoir is possible. And it could also be internal: lines on the inboard side of the firewall, a vacuum actuator, or the controller itself. But most of the time you'll find the problem under the hood, in the not-so-nice environment.
If you have a small vacuum leak everything still works fine at idle, but when you accelerate and engine vacuum drops, the "air mode door" will go to it's default position, up top and out the defrost ducts.