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Old 06-11-2013, 04:00 AM
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Another defrost issue thread...

I am not just posting this without thoroughly reading and searching not just our forum but many others and my problem still persists so I do need your expertise!

The truck with these issues is a 00' 2WD...
Finally got the A/C system fixed after being broken for 1+ year (by fixed I mean it took the entire mehanical system, condensor, evaperator, dryer, compressor, manifold lines, clutch fan, etc...) Everything works very well except for the dang old vent failure to defrost that seems to happen to everyone at some point.
Here is the run down of symptoms and what I have tried.

Symptoms: ONLY after driving for 10 min+ the vent air will slowly change to defrost only, if I turn the function selector to the "OFF" position and let it sit for 30 seconds then turn it back to Vent, A/C, or Max A/C it will work good again for a couple of minutes and then begin the process all over.

Fixes already tried:
1.) I have made sure the vacuum pump is operating properly, it turns on when I disconnect a vacuum line and from a completely empty vacuum resevoir it only takes around 90 seconds to fill the system and turn back off.
2.) I have used the soap and water method to check ALL the HVAC lines, from the vacuum pump and resevoir into the dash and even tested the vacuum actuators under the dash and have found no leaks.
3.) I have replaced the function selector switch as I found a slight leak inside the vein for the vacuum control.
4.) I have replaced the EGR and MAP sensor lines and made sure they were clamped with no leaks.
5.) It is 2WD so there are no hub lines to be concerned about...

The problem is still present though and with 97 deg. days on me here in south Georgia I want this resolved!
So what am I missing? I read somewhere on some forum that the EGR solenoid could be leaking? or MAP sensor? those arent expensive to get but I am tired of trial and error as the test drives to duplicate the problem take time!

P.S. When I replaced the MAP/EGR lines I found a hole in the MAP line and after that replacement I can feel a difference in vent system (you can tell the vacuum doors are closing all the way when first used) and I can tell that leak was a major part in this ordeal but after use the system still leaks back down.

Thank you for any help guys!!

Last edited by ThomasvillePavers; 06-11-2013 at 04:01 AM. Reason: Spelling error
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Old 06-11-2013, 08:13 AM
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Update: Borrowed a mityvac vacuum tester and was able verify the vacuum pump and resevoir pull to 15 psi then cut off, pump kicks back in at 12 psi and only takes 31 seconds to pull back to 15 psi cut off.
The black vacuum feed line going to the HVAC system holds 15psi even with no drops for 20 minutes, same as the pump/resevoir.
I also set vacuum to the engine side direct vacuum to the wastegate bleeder solenoid thing and it kept 15 psi also.

I am wondering after reading some more searches if that solenoid (on the CAC with the green to intake and red to wastegate/manifold lines) is a wastegate/vacuum bleeder or run off could that possibly be failing me and staying open? can I just disconnect it (the wastegate is disconnected already) so it really serves no purpose to me if that is its job!
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Old 06-11-2013, 08:29 AM
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have u checked the actuator behind the glove box ?

but I think the actuator should have a constant vacuum to send it to vents so it seems like you may be dropping vacuum

u can test at the actuator and signal with a cheap harbor freight gauge or a mighty vac
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Old 06-11-2013, 08:36 AM
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Yes I have tested the actuators under dash and all of the HVAC vacuum lines, all are good. I agree with you that I am losing vacuum while driving and after testing now I believe it to be on the engine side (which is apparently very minimal lines) the waste gate solenoid appears to be the vacuum from engine
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Old 06-11-2013, 08:51 AM
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not sure on the wastegate and there should be no vacuum from the engine ??
but not familiar with your motor


not sure what I would do even a small leak should be compensated for by the pump

i would maybe start by using the mighty vac on the actuator to get it to vents

and see how long it holds that position ?


make sure you block the line coming from the pump



i was pretty sure the actuator needed the vacuum present to choose between the vent positions ( varied strength ) and if vacuum is lost it goes to defrost

but I am not 100 percent sure on that
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Old 06-11-2013, 09:18 AM
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Your right on the money about no vacuum = defrost, I am goin to hook the mityvac now to the vacuum supply heading into the dash and then place the function selector switch on vents and see how long it holds
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Old 06-11-2013, 10:55 AM
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I think I am at a dead end now...
I just connected the mityvac inbetween the resevoir and main vacuum feed line to interior HVAC turned the key on and let the vacuum pump pull until it shuts off at 15 in. Then turned the function selector switch to Max A/C and let her sit for over 1hr and it never dropped from the 15 in.

I am stumped now and do not know what could be causing it!
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Old 06-11-2013, 04:31 PM
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After driving home from work, the normal drive where the a/c acts up numerous times, I think somehow while foolin around today and looking for the problem I actually fixed it! It worked great the entire afternoon... It was either a poor connection on the vacuum lines or somehow the waste gate solenoid that I bypassed was the culprit
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Old 06-11-2013, 05:30 PM
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just thinking out loud. do you think a vacuum line is weak and collapsing after a constant pull is on it?
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Old 06-11-2013, 05:41 PM
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Quote:
Originally Posted by gomer pyle View Post
just thinking out loud. do you think a vacuum line is weak and collapsing after a constant pull is on it?
while that may not be the issue since they are ""mostly"" hard lines that is a damn good concept
and there probably are a few transition fittings that could do that

Last edited by ZMANN; 06-11-2013 at 06:04 PM.
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