I have been busy stripping my third Series III XJ6 parts car, a 1987 XJ6, of the remaining good parts before I have the carcass towed away. I have been disassembling the dash and after I removed the heater blower motors I discovered that both flaps on one of the blower motors were inoperative due to a failed vacuum actuator (RTC1914). I removed the failed actuator from the heater blower motor and cut it open with my dremel to find the reason that it failed. You will see in the attached pictures that the rubber diaphragm had failed and had a few slits in the rubber that leaked vacuum. I replaced the vacuum actuator with a spare used one that I had on hand from one of my other parts cars and returned the flaps on this heater blower motor to full operation again.
I am posting this so that others can see that this failure happens and that a failed diaphragm keeps the outer flap open at allowing outside air in the cabin at all times. This may not be a big thing in warmer climates, but in the middle of winter in some parts of the world cold outside air in the cabin at all times is not a good thing.
The only way to remove and replace the vacuum actuator is by removing the heater blower motor from the car, which is a complicated and time consuming thing to do.
Picture #1 shows the heater blower motor with the outer flap open and vacuum gauge at 0 showing the vacuum leak.
Picture #2 shows the vacuum actuator on my vise prior to disassembly. Picture #3 shows the vacuum actuator disassembled after I cut it open with my dremel. Picture #4 shows the slits in the rubber diaphragm that leaked vacuum. Picture #5 shows the same heater blower motor after I removed and replaced the vacuum actuator with the outer flap closed, the inner flap open, and vacuum being held when applied with my Mityvac.
If you are having problems with your climate control system flaps not operating properly it could be due to a similar failure. The vacuum actuator has a sealed metal cover over this diaphragm so the failure in the rubber is likely due to age. I suspect that there may be a bunch of failed climate control vacuum actuators (there are a bunch of them in each car) like this out there. Hopefully this post will help others.
BTW, one of the more enjoyable parts of my Jaguar hobby is learning how things work, discovering why things don’t work properly, and fixing things that are broken to return them to proper operation again. So this was a lot of fun for me.