1989 XJS, HVAC system seems to work as expected though I've read that factory they were kinda quirky (cold AC air on feet).

Two problems:
1. (assume fan speed on high, temp to coldest setting) with more than 1/4 throttle the center vents cut out, i.e., stop blowing, as soon as throttle is released they blow again.
2. with fan to high speed, there is a high pitched squealing in upper dash area, behind the gauge cluster. It sounds like a goose being strangled. It goes away after a few minutes and does it regularly (every start up).


I don't think the noise is the fan motor since its not constant and starts and stops so regularly. I also sprayed WD40 into blue intake hose before the fan hoping that I'd get lucky (if its the fan) but no difference.

problems related? ideas?

 

This sounds to me like the vac supply/reservoir/pipes to these are leaking, and/or the one way valve is stuck open. Under the bonnet on the firewall area between the water valve and the US passenger's side you will see a one way valve in the vac line. It has a push fit onto the vac line each side and a wide round middle piece. See if this is working or not. If not you may be able to unstick it/replace it if needed.


The actual vac lines themselves may be leaking vac. Take a good look and replace all of them if the one way valve fix does not solve the problem. They come off the inlet manifold spigots at the firewall end of the manifold. Finally, under a plate on the US passenger side engine bay, where on the driver's side the pedal box and brake servo are fixed, is the vac reservoir. Undo the plate and check that the pipes attached to this are still attached and that it holds vac. If it does, you should hear a hiss when you pull off the pipe.


Note that there is more than one pipe going through this plate. One goes direct to the HVAC unit from the water valve, to close it when full cool is dialled in the cabin. look at this pipe as far as you can too. I think the squealing you are hearing is either the water valve vac operation not working, or more likely, the non return valve. The reason the HVAC unit works properly, foot off, is that then vac is getting to the unit from the manifold. Foot on, less vac in the manifold, and the vac reservoir and one way valve, between them, have no vac supply to activate the HVAC unit's flaps.
Greg

 

Excellent info, gonna take a look and report back.

 

Greg for the win!


How about NO one-way valve on the vacuum line running to canister under the dash?

Some idiot owner (me) obviously took it off when changing vacuum lines and left it off. Installed one and noise appears to be gone (it was random). Will report back to confirm but that appears to be fix.

Thanks! Never woulda figured that one out.

 

Glad it all works now, Andy.
greg

 

Spoke too soon...

Turns out it was a coincidence, same time I added the vacuum valve the noise stopped--but it always eventually stopped.

After the car sat for a few days noise is still there. Took apart the lower dash panels and have now traced the noise to the blower motor. It squeals for a bit and then eventually gets quiet.

No way I'm taking the drivers side dash apart (on LHD) car for a noise that lasts for a few seconds. Sooooo...

I drilled an access hole in the fan housing and sprayed several lubricants (WD40, white lithium grease, Dry Lube spray) into the housing using the 4-way spray nozzle from the product below. I'm hoping that somehow, someway a bit of lube makes its way to the offending squeak. I'll also be going to church on Sunday.

 

Eastwood internal frame coating.