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JOHNFAK

Ac vents not working

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Look closely the red in mine is the vacuum motor near the trans hump. The yellow is the one up on the firewall.

So the red and yellow and black all tee off into some nipples and they all seem secure. Any other ideas ?

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Is the output stuck on defrost? If so this is the default mode, if the system fails. I've heard that one must pull the dash to change to module. (What a stupid way to build a system) Mine is stuck as above until I hit the lottery... My nephew crauled under the dash with his long arms and was able to flip the lever to the dash setting but of course it didn't stay.

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Is there vacuum up to that point? If you separate the coupler and put your finger over the connectors is there vacuum? Then I would check at the control in the dash is there vacuum there?

Pulled the red, yellow and black wires off and no vacuum. So going to have to track it back further ............... where to now ........ What I dont get is this always worked fine and I still have vacuum in my CAD and cruise .........

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Vacume pump is on the drivers side, backed up to the power steering... I think on mine, the vacume line went back to the firewall then across above the engine with the harness on the cowel edge before going through the firewall. Some Ts & connectors... Lots of places a tube could crack or a coupler slip off or get dry rot.

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Exactly... There is a loss of vacuum for sure on the HVAC system that why there is no vacuum. The source vacuum should be on the black tube. All other tubes are function tubes in other words they are slected as you twist the knob. So if the black line going back out the firewall is damaged then there will be no vent controls. As for the vacuum pump is strong enough to over come a leak and still keep other feature working yet. (CAD and Cruise control)

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As for the vacuum pump is strong enough to over come a leak and still keep other feature working yet. (CAD and Cruise control)

This was my bad assumption. I figured if I had vacuum for CAD and cruise then must have vacuum for vents. So not a vacuum issue. Seems on some other forums I found threads where same issue as me and turned to be a leak. So will be chasing it down over next couple days. thx guys
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Like on MoparMom's 96... The vacuum line to the cruise control was cracked but the cruise still worked for the most part but the vents would default to DEF every time I'd climb a hill. So I just finally gave up and replaced all the tubing under the hood to kill this problem. Because I was chasing the HVAC when it was the cruise control that was the cause even though it still worked. :banghead:

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Ok found one hole and replaced that part but no diff. If I blow onto end of vacuum by the ac. I can feel the air going through no resistance so must be another leak Guess I can't use compressed air on the lines as may blow vacuum seal ?

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How hard is it to spot damaged lines? Can you see the flaws or feel a crack or rough spot? This would help allof us troubleshoot this problem system.

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In that first pic Mike posted on the very top on the left, that yellow line runs to that actuator diaphragm.. That is the one that opens the regular vents. Mine will do everything but run that actuator but it has enough vacuum to hold it open so I just reach up under there and push it by hand and then it holds in place. Just in case you were desperate..vise grip that one or something. There is in Mike's pic and another line goes back all the way through the firewall and back to another T that is by the brake booster on the firewall. You could start at that T and work your way up to the T under the dash.

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But there's no vacuum comming to the yellow wire so how will vice gripping it help - lost that bit If I blow air down the tube going to vacuum motor by power steering there is little resistance like it keeps taking more air ? Normal ? Don't know if there is a check valve or anything to prevent that anyway Trying to see which line from on top of the firewall then goes inside the cab ...

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Not really there is no way to access the vacuum lines unless you pull the dash back in the passenger side. Sorry John...

NO worries I figured as much. Gives me an excuse to finally replace my dash on year ..... I have enough line to create a connection - but cant lose anymore :) Why does the line have so many funny shaped couplers running along the firewall - eg wher ethe 90 degree bend is and a couple other places - rather than just a single normal line with a couple tees split off it ? If you follow me ...... Im going to get rid of the 90 degree coupling for example comming off the condensor and reroute around teh hot parts but wondered why all the funny coupling - since no special purpose ? I'll post a couple pics

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If it was me I would replace all the tubing under the hood with new vinyl tubing from a hardware store and not look back. :whistle:

Yeah - pretty much have now :thumb1: Thanks team MM ......... got it done ...... good to have vents back ....... plugged up a couple holes on my windshield washer reservoir also .....

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Glad you have it fixed. I have found on the wifes 300SD that a mity vac and a vac gage are your best friend when it comes to vacuum leaks. Everything on that car is controled by vacuum. It even runs through the ignition switch, because the fuel shut off on the fuel pump is held open with vacuum, so when you turn the ign. switch off it shuts the vacuum line going to the fuel shut off.

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