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Auxillary Rear A/C


February 22, 2015
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Year, Model & Trim Level
2004 Mercury Mountaineer
This was done on a 2004 Mercury Moutaineer

If your Front A/C is blowing cold, but your rear auxillary is blowing warm.

1. Check to make sure blend doors in rear unit are functioning correctly, there are two one is for the Hot/Cold and the 2nd is for the ceiling/floor vent.
2. Check to make sure the system is full, system requires 56oz of R134, consult with your label under the hood to verify yours is the same

I suspect the TXV(rear expansion valve) is not working correctly. The valve has a bulb attached to the cold side and is attached between the cold and hot lines. To get to it you need to remove the left rear panel.

You will need to evacuate the system since the front unit and rear unit share the same compressor. The contents are under high pressure so always take the proper safety precautions. Once the system has been evacuated, I would also suggest replacing the orifice tube and accumulator.

Once the parts are changed, you can then have someone evacuate the system again, check for leaks and fill the system.

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With rear AC, there is a secondary filter (similar to the orifice valve, but just a screen) located in the AC line behind the rear wheel on the drivers side. With an empty system, disconnect the line as it enters the vehicle, using a flashlight, look into the line you disconnected and you'll see it.

When I replaced my system, the front orifice was as clean as new, but the rear filter had crud caked in it.

If you leave this secondary screen in without changing it, you'll either end up with reduced cooling in the back, or a bad compressor if the gunk makes its way back.

Compressor has finally had it, so when I open the system backup, I will take pics of the screen in the rear ac line.

2002 2003 2004 2005 Explorer rear AC filter screen

Here are some pictures of the rear filter etc.... When I was doing this originally, no one could tell me where the rear filter was. I almost missed it because you can't make it out in the line very well.
In the picture looking into the disconnect line, it's the black o-ring looking thing. I pushed a small (tiny) flat head screw driver into it to remove it.


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I also replaced the rear expansion valve which had it's "temp detection probe" attached to the line with foam. I used MMM Strip Calk 08578 to attach the new one. I tried to put it in the exact formation as original, as it wasn't originally completely covered.

This strip calk is pretty handy. Where I've drilled through the firewall for wires, I've used this stuff to plug the hole.

One thing I found interesting, was the rust or corrosion on the inside of the original compressor.


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Just confirming, from the pics above the filter is in the high side line.

The line closest to the rear I believe.

I'd disconnect both lines from the rear (where they enter the car,) then from the front use compressed air to blow out the lines.

Fwd ac line filter (orifice tube) under hood

Hi guys thought I would add to this thread by adding a photo of the other in line filter going to the front evaporator this is also inside the line needed to pull this out with angle needle nose pliers . Mine had some small metal filings on it cleaned with brake cleaner.


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Fwd filter


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