I'm working on my 74XJ12 with the Delanair II and think I've got AC finally working.

But I hear an occasional noise, it sounds like a metal flap clanking/hitting in response to the throttle movements while driving. It also makes the noise when I shut the car off so seems to be directly related to engine vacuum disappearing.

All my dash vents appear to operate correctly and AC works pretty good. I dont hear a vacuum leak in the car. But I did take a bunch of stuff apart and I'm wondering if this my own creation or something else.

Any ideas of where to start to look?

 

Andy
That symptom relates to vacuum not being held properly. There should be a non-return valve between the manifold vac takeoff for the aircon reservoir and the reservoir. It should be in the vac line in the engine bay along the firewall somewhere, and may have stuck open.
Or, the vac reservoir or some of its pipes may have failed.

 

it it a "cowbell" noise when you shut the doors?

that noise is caused by the 4 ventilation flaps located in the trunk / boot channel.

Open the trunk lid and at the top of the channel behind the rubber seal you can see rectangular cutouts.

Behind those cutouts there are flaps hanging. The factory glued headlining fabric to each flap to prevent metal-to-metal noise. When the glue dries, the fabric buffer falls off and the flaps make the noise.

the flaps are attached to a water-collecting pan bolted under the rear parcel shelf at the trunk. Remove the pan, clean the years of debris and glue thin foam pieces to each flap.

 

Sorry for long delay.

I think that may be the problem. I checked the vacuum tubing set up and realized I put the non return valve in the wrong place. I had it between engine and air con system but after the vacuum reservoir so the reservoir wasn’t filling. See pic below.



the red line is engine vacuum, the blue line is to reservoir, and green is to air con. This is how I had it originally. I’ve since moved the one way valve between the engine vacuum port and the tee fitting so now air con and reservoir are connected.

but I haven’t tested it yet cause it just started raining but fingers crossed. 🤞

 

I don’t think that’s the noise but I checked that area and discovered the drain lines were cracked so you saved me from a problem I didn’t know I had!
now I’ll check out that pan

 

the fresh air ( open ) and recirculation
(closed) Flaps in the blower fan Cases have foam rubber seals that dry out and then you have metal-to-metal contact as well as vibrations.

To check, go near the floor on each side and tap the flaps to hear any metallic noise when the flaps are closed.

There are two flaps per blower case, the one facing the floor, and one that cannot be seen unless the the blower case is removed from the interior of the car.