With the temp on 65 and the fan on high, why does the center vent stop blowing air when I accelerate? It seems pretty consistant. As soon as I let up on the skinny pedal the vents open and it blows air again.

Also is there an easy mod to get directional vents in the center vs the one that just blows to an empty back seat?

 

I'm not an expert on Jaguars, but that's a pretty commom symptom of a vacumm leak. Maybe just a cracked hose.

 

Yeah, loss of vacuum. Test the black/white check valve that's over by the battery...you'll see it in the vacuum line. You should be able to suck thru it in only one direction.

Cheers
DD

 

Doug - Thanks, that's kinda what I thought it might be, but had no idea where to start.

Any thoughts on getting a center vent that you could divert the air to the front passengers with?

 

Looks like that valve is going bad. It will take a vacuum, but not hold it. Is there a common replacement for that CAC4188 valve? I'm searching but have found a definative answer.

 

Just ordered a replacement from MotorcarsLTD for < $8.

 

No cigar......The center vent still closes under acceleration.

Any other thoughts?

*** Update : With the car in Drive and foot firmly on the brake I can see the flap starting to close ~ 1,000 rpm. It opens back up when I get south of 1,000 rpm.

I'm going to double check the transitions off that line to see if they are holding. They are kinda sketchy looking.

How much vacuum should be in that line?

 

It should have vacuum similar to what the engine vacuum is at idle. The actual amount is not critical as long as the flap works. The vacuum supplied by the engine diminishes as the throttle opens under acceleration. The check valve is designed to seal off the vacuum in the lines when the engine isn't supplying it. If the lines, check valve, or vacuum actuators allow any leakage, the flaps won't stay in the correct position. Use a vacuum pump to apply vacuum to sections of the system using a vacuum diagram to isolate which section is leaking. Connect the pump to a section that should be sealed, pump a vacuum, then monitor the gauge on the pump to see if the section holds vacuum or leaks down. If it leaks, you need to subdivide the leaking section and seal it off as needed with plugs so it can be tested in smaller sections until a leak is found. You can connect the pump directly to the actuator and apply vacuum to see if its diaphragm leaks down.

A small leak would allow the system to work as long as engine vacuum is present, but as soon as the vacuum supply is gone, the leak allows the vacuum level to drop off and cause problems.

You need this guide to help you troubleshoot, it has well-done color diagrams, and is unfortunately no longer available on the original site where I found it:
Click here for the AC Schematics-mk2 Delanair.pdf

 

Thanks for the link! It is much easier to read than the workshop manual.

The alt install and rain got the better of my time this weekend.

However today at lunch I plugged in my vacuum gage in place of the line running to the AC. Brake torquing up to over 1k rpm showed that the check valve and vacuum accumulator are functioning.

Maybe tonight I'll be able to check further.

 

You're welcome. I went ahead and posted some of my other Jaguar stuff on my SkyDrive here if anyone needs it:
Jaguar Info on SkyDrive

 

I got a chance to do a little more troubleshooting today. I found that the vacuum line to the blower I replaced had come undone. I added a new bit of line to give me enough room to plug it back in again and everything came back to life.

What a difference that made to the AC. Now that the air was being pulled from the proper location it really cooled off. Scratch the plans to get it recharged! Woohoo!

Thanks for all the help.