1999 Crown Victoria slow knocking sound from the dash

[anitak1982]

I keep trying to google what this could be and keep coming up with everything but what I search for. It isn't a clicking sound but a sound like something inside is knocking slowly. It happened when we tried to switch from heat to the air conditioner. it is a very old car and the miles are low and the body condition is great. But we fear this thing is a money pit anymore.

[Parnassia]

There are multiple web forums devoted to Crown Victorias. Why not join one?

Just one:

https://www.crownvic.net/ubbthreads/ubbthreads.php

[grampaTom]

Originally Posted by anitak1982

I keep trying to google what this could be and keep coming up with everything but what I search for. It isn't a clicking sound but a sound like something inside is knocking slowly. It happened when we tried to switch from heat to the air conditioner. it is a very old car and the miles are low and the body condition is great. But we fear this thing is a money pit anymore.

I'm thinking a vacuum switch in the heating/AC system is leaking or stuck.
I had a GM product that did the same thing. I finally learned how to switch it to AC or heat manually but it was a chore so I only did it spring and fall.

[Labonte18]

Originally Posted by grampaTom

I'm thinking a vacuum switch in the heating/AC system is leaking or stuck.
I had a GM product that did the same thing. I finally learned how to switch it to AC or heat manually but it was a chore so I only did it spring and fall.

Was '99 still using the vacuum method? If so, I agree. I was going to say it was trying to open/close a blend door that was stuck or something and that 'thump' was the door hitting.


Possibly more expensive to fix than its worth.. Not sure how difficult those things are to get to on that vehicle.