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HVAC mode actuator location


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My MJ is stuck on the defrost vents. The useless manual I have had nothing with actual locations of vacuum actuators. I need to test it, and try to find a replacement if it's faulty.

 

I'm about to do a compressor, accumulator, expansion block, flush, 134a conversion, blower resistor, and duct cleaning.

 

Can someone please give me the exact location of the mode for actuator?

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Defrost is the HVAC default when you have a vacuum leak. Normally this happens where the plastic vacuum line passes through the front bulkhead to the vacuum canister behind the bumper. Check this plastic line from the firewall all the way out for leaks.

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There are several actuators, one for each "mode door". They're all mounted on the left side of the HVAC box, except for the recirculation door. As Don said it's more likely you have a vacuum issue, as the air will blow out of the  upper defrost vent if no vacuum is available.

actuators.JPG

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The problem is almost certainly where the vacuum line runs from the vacuum reservoir behind the front bumper under the battery tray. The hose deteriorates, a vacuum leak developes, and with no (or low) vacuum the vents default to the defrost position.

 

It could also be a leak in the reservoir canister itself.

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The problem is almost certainly where the vacuum line runs from the vacuum reservoir behind the front bumper under the battery tray. The hose deteriorates, a vacuum leak developes, and with no (or low) vacuum the vents default to the defrost position.
 
It could also be a leak in the reservoir canister itself.
So I tested that section with my vacuume pump & gauge. Pump down a vacuum, and check the gauge for loss. I tested it at the T up by the firewall. No vacuume loss. I decided to check it again and found that the previous owner had removed the canister, and capped off the line just forward of the battery.

This guy cut more corners, and did more shady work than I've ever seen before.
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That's the problem, then. Under light throttkle the engine has enough vacuum to hold the actuator doors where you set them but when you accelerate or go up an incline, as you know the throttle opens and the engine vacuum drops. The canister is a vacuum reservoir to maintain vacuum under those conditions.

 

You can get a canister from any wrecked XJ. There are two types -- the ones with cruise control have two chambers, one for the HVAC and the other for the cruise control. If your truck doesn't have cruise, you can use either type.

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26 minutes ago, GreasemonkeySC said:

So I tested that section with my vacuume pump & gauge. Pump down a vacuum, and check the gauge for loss. I tested it at the T up by the firewall. No vacuume loss. I decided to check it again and found that the previous owner had removed the canister, and capped off the line just forward of the battery.
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This guy cut more corners, and did more shady work than I've ever seen before.

HAHAHA I had the same issue with my $400 XJ.  It seemed he went out of his way to do poor repairs.  Just one example, he cut one of the support rods for the wiper transmission assembly, I suspect because he couldn't figure out how to get it out.  Then he taped it back together with electrical tape (yes, yes he did).  Me, wondering why the wipers are out of sync....hmm, never seen this before.

 

And I had a leak at the vacuum ball... defrost only.

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Gonna make a new vacuume reservoir tomorrow. I've got an old stainless water bottle that's not the insulated kind. The lid has a very good thick seal on it, so I'll put an 1\8" barb through the cap, hose clamp it somewhere, and connect to the existing vacuume line.
Redneck, I know, I know...... But the one I made from an empty R134a can has been in my Rubicon for about 8yrs without fail!

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On 7/19/2018 at 3:28 PM, schardein said:

Just one example, he cut one of the support rods for the wiper transmission assembly, I suspect because he couldn't figure out how to get it out.  Then he taped it back together with electrical tape (yes, yes he did).

 

And I had a leak at the vacuum ball... defrost only.

You wind the award for this year for finding the most hillbilly auto repair done by a previous owner!!

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  • 3 weeks later...



You can get a canister from any wrecked XJ. There are two types -- the ones with cruise control have two chambers, one for the HVAC and the other for the cruise control. If your truck doesn't have cruise, you can use either type.


Finally got time to install a temporary vacuume canister while I sort out the problems.

BTW: still no vacuume leak, and mode stuck on defrost. a514edc05c83418ebb2ee7aaca784302.jpg
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