Possible Vacuum Leak

[1997ThunderbirdLXV6]

Here's the observation: recently when I get into the car first thing in the morning, and I turn the A/C dial to "OFF" (as I habitually do before starting the engine), I hear...nothing at all.

I used to hear the recirculation door close. In other words, the vacuum in the system was maintained overnight.

Now I hear the door as the engine starts.

Functionality while the engine is running is normal, so I suspect a small/tiny leak. Where should I look? I imagine there are a few check valves along the way between the intake and the A/C system (?).


Meanwhile, also recently, I have the impression of slightly increased fuel consumption. I'm not entirely sure really; this may be due to my recent move. Just mentioning it as an aside.

 

[1997ThunderbirdLXV6]

Bumping this months-old question. Anyone?

 

[theterminator93]

The HVAC vacuum canister is mounted to the upper frame rail inside the passenger's inner fender area near the firewall. There is a check valve near the firewall inside the engine bay near the A/C accumulator that tees to manifold vacuum to the vacuum canister and the HVAC head in the cabin. You could start from there to isolate where the leak is.

 

[1997ThunderbirdLXV6]

Ok...I'll investigate.

But since you're mentioning a check valve, is it safe to assume that a vacuum leak inside the cabin would  not affect any vacuum-driven stuff in the engine compartment?

 

[dDUBb]

Ok...I'll investigate.

But since you're mentioning a check valve, is it safe to assume that a vacuum leak inside the cabin would  not affect any vacuum-driven stuff in the engine compartment?

No .. the check valve allows the vacuum to remain inside the cabin when engine vacuum decreases. A vacuum leak inside the cabin would certainly affect the engine.