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1988 Xj: HVAC Control Provides only Defrost

RAVC1

NAXJA Forum User
Location
Michigan
It appears I no longer have vacuum (at least at the manifold on the back of the HVAC control unit in the dash) according to this reference thread

http://naxja.org/forum/showthread.php?t=1143023

Unfortunately, I have been unable to locate the leak so, I need to remove the radio (above the HVAC control) or the entire dash because, the inspection of hoses in the engine compartment did not show me an obvious culprit.

The vacuum reservoir in the front bumper appears fine and so do the rubber lines from/to it. What should vacuum be (at given engine operating conditions be?).

With this in mind, I may have lost a related problem or symptom. That is, my valve cover began being soiled as the breathing lines were clearly being pressurized some time after I purchased the car. Note the engine did not soil the valve cover initially. When I posted this issue on NAXJA everyone suggested the small valve cover port was blocked yet, this was not (an never has been) the case.

Any ideas regarding the (potentially related) issues?

Has anyone figured out what we can use to replace the fitting in the TB housing the MAP sensor line fits into? The only suggestions I have been able to come up with is a custom machined part.
 
On my 97 the cause was a broken vac line about the size of those stir straws you get with a cup of coffee. Broke about a inch or 2 before it passed through fire wall and was blocked by my wire harness so I couldn't easily see it
 
The HVAC system vacuum lines have almost nothing to do with the engine operation vacuum lines. The CCV system and the MAP line will not cause any HVAC issues. The only commonality is the SOURCE vacuum line from the rear half of the intake manifold. If that line is good...all the way to the vacuum reservoir...you are OK.

The leak causing the HVAC to default to defrost is more likely at the vacuum reservoir, the source line, the cruise control vac line or the lines coming out of the firewall.

Also, the "fitting" on the TB from the MAP sensor is just a keeper. There is only one hole that goes into the TB there. A single plug line will do the same thing. If you can't find it at the dealer, pick one out of a donor at the junkyard...a pocket item at our yards.
 
The HVAC system vacuum lines have almost nothing to do with the engine operation vacuum lines. The CCV system and the MAP line will not cause any HVAC issues. The only commonality is the SOURCE vacuum line from the rear half of the intake manifold. If that line is good...all the way to the vacuum reservoir...you are OK.

The leak causing the HVAC to default to defrost is more likely at the vacuum reservoir, the source line, the cruise control vac line or the lines coming out of the firewall.

Also, the "fitting" on the TB from the MAP sensor is just a keeper. There is only one hole that goes into the TB there. A single plug line will do the same thing. If you can't find it at the dealer, pick one out of a donor at the junkyard...a pocket item at our yards.

No longer available new.

Here's a solution:http://cruiser54.com/?p=280
 
One of the small diameter vacuum lines directly behind the passenger side head lamp and a small hole in the vacuum reservoir were my culprits. Fortunately, I was able to repair both leaks this morning and find a replacement formed coolant hose to replace the "J-shaped" hose between the manifold (that connecting the larger front PCV port to the air box) and the air filter cover (Car Quest/Advance Auto #87618).

I am uncertain if my PCV system is operating correctly with the superficial level of testing I have performed but, I do have Heat/Vent/Defrost air flows now that vacuum has been re-established.
 
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