Vacuum leak under dash.

Lando · 07-11-2012, 03:49 PM

89 780 b230ft

I have had issues with the climate control defaulting to defrost when the engine is in boost. I checked both of the check valves for the vacuum lines that go through the firewall (the ones by the drivers side strut tower). I notice one sounded like a kazoo before it closed and was a little slow to close, but still seemed held pressure. Replaced them both with volvo NIB units anyways.

This has helped to slow the onset of defaulting to defrost, but it still happens after about 20-30 seconds of boosting. Quite annoying on highways or going up hills.

I pulled the glove box and kick panel on the passenger side and tried to listen for the leak. I could not hear it. I examined the little kong looking vac reservoir and it looked ok. All the vacuum lines were attached. I fear the actuator is leaking from the diphragm. But just wanted to get some input from you guys.

Where do these systems usually leak? Hard to trace since I cant hear it.

vlvman · 07-11-2012, 05:29 PM

My 89 740 had a large vacuum reservoir right behind and inside the front bumper. I don't know if yours has it are not but it might be worth looking for and checking for leaks in those lines.

TrickMick · 07-11-2012, 05:38 PM

can you plumb a plastic "TEE" into the line going to the actuator and use
your vacuum gauge to see if it IS "losing vacuum"??

Lando · 07-11-2012, 10:47 PM

Quote:

Originally Posted by TrickMick

can you plumb a plastic "TEE" into the line going to the actuator and use
your vacuum gauge to see if it IS "losing vacuum"??

I certainly could, but I didnt have many of my tools with me when I got down to it. I'll check that out tomorrow.

Vlvman, wouldn't the check valves isolate the in dash part of the system?

vlvman · 07-11-2012, 10:57 PM

Yes, they should. I think the reservoir behind the bumper was T'd in after the check valve, giving the heater system more capacity. Is the reservoir under your dash a small one? Adding a larger one might be a easier way to solve the problem.

Lando · 07-11-2012, 11:00 PM

Thanks for the tip I'll look into it.

Lando · 07-12-2012, 02:01 PM

Vacuum tested the servo and the vacuum reservoir independently and they each hold vacuum, but when I tee into the system, it loses 20in hg in about 20 seconds. I still cannot hear the leak any where under the dash.

Does any one have a diagram of the system? Vlvman do you have a picture of the extra vacuum reservoir that is under the bumper. My airdam is gone and I still can see it.

TrickMick · 07-12-2012, 02:18 PM

from KJet - *700*
try page 206 of TP31127-1 "700 BODY FITTINGS incomplete*

vlvman · 07-12-2012, 06:02 PM

Sorry no pics, sold that car, it was inside the bumper cavity. If you can apply about 5 psi air pressure you might be able to hear it easier.

07-11-2012, 05:29 PM	#2
vlvman Board Member Join Date: Mar 2009 Location: Jefferson City, MO	My 89 740 had a large vacuum reservoir right behind and inside the front bumper. I don't know if yours has it are not but it might be worth looking for and checking for leaks in those lines. __________________ Robert http://www.volvowiringdiagrams.com/ 82 244DL, 2004 S60R AWD, 2008 S40 GF's Had: 77 242 DL, 80 242 DL, 82 245 DL, 89 740 GL, 94 850T, 95 850 GL, and a 02 S60 2.4T

07-11-2012, 05:38 PM	#3
TrickMick Board Member Join Date: Jan 2011 Location: norte carolina	can you plumb a plastic "TEE" into the line going to the actuator and use your vacuum gauge to see if it IS "losing vacuum"?? __________________ In a closed society where everybody’s guilty, the only crime is getting caught. In a world of thieves, the only final sin is stupidity.

07-11-2012, 11:00 PM	#6
Lando Hunting with Ray Charles Join Date: Mar 2011 Location: SL UT	Thanks for the tip I'll look into it. Last edited by Lando; 07-12-2012 at 02:00 PM..

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07-11-2012, 10:57 PM	#5
vlvman Board Member Join Date: Mar 2009 Location: Jefferson City, MO	Yes, they should. I think the reservoir behind the bumper was T'd in after the check valve, giving the heater system more capacity. Is the reservoir under your dash a small one? Adding a larger one might be a easier way to solve the problem.

07-12-2012, 02:01 PM	#7
Lando Hunting with Ray Charles Join Date: Mar 2011 Location: SL UT	Vacuum tested the servo and the vacuum reservoir independently and they each hold vacuum, but when I tee into the system, it loses 20in hg in about 20 seconds. I still cannot hear the leak any where under the dash. Does any one have a diagram of the system? Vlvman do you have a picture of the extra vacuum reservoir that is under the bumper. My airdam is gone and I still can see it.

07-12-2012, 02:18 PM	#8
TrickMick Board Member Join Date: Jan 2011 Location: norte carolina	from KJet - 700 try page 206 of TP31127-1 "700 BODY FITTINGS incomplete*

07-12-2012, 06:02 PM	#9
vlvman Board Member Join Date: Mar 2009 Location: Jefferson City, MO	Sorry no pics, sold that car, it was inside the bumper cavity. If you can apply about 5 psi air pressure you might be able to hear it easier.