Expansion Valve Replacement
The front expansion valve is accessible under the plastic rain shield at the base of the windscreen on the left (driver's side on the US cars). It's the aluminum block that sits between the ends of the AC lines and the ports on the evaporator. Has a little diaphragm and a small coiled copper cap tube on the end towards the fender.
To replace it, you'll want to first evacuate the gas from the system. The air cleaner box needs to come off completely, and the clamps that hold the lines to the firewall need to be removed. On my '89 the ends of the tubes are retained by clamp plates that bolt through the aluminum valve block. Earlier cars may have threaded nuts over each line according to the repair manual. There are o-rings at each port that need to be replaced with the valve. The replacement valve I got from David Roberts has the o-rings included, by the way (shameless plug...) Anyway, it took me a little bit of pulling and prying to get the lines clear of the valve from the firewall side, but it really can be done. Install the new o-rings and the new valve, restore all the clamps, the air cleaner parts and the tubes. Evacuate the system and recharge.
If the drier has not been replaced recently, now is a good time. Even a partially contaminated drier has a negative effect on system performance. If the expansion valve has crud in it, that means that your old drier isn't doing the job. These are relatively inexpensive parts, especially if you are recharging the car with R-12.
One interesting thing I noticed is that little section of suction tube behind the engine where the fuel return line is attached. Looks like the factory has cut down on the hot fuel return problem by sharing some of the heat with the AC system. Clever, undocumented, and a bit of extra load on the system.
There's also an expansion valve at the rear evaporator on the dual air cars. If you are doing the front, the rear should probably be changed too if you use that unit. Procedure is the same, with the valve mounted directly to the pipes of the rear evaporator. Right rear seat back needs to come out for best access, and the cover from the unit unscrews once the vent grills are removed.
Hope this helps!
I used Dr. Bob's post as a guideline for removal of the front expansion valve, and it was very helpful. Without taking any credit away from Dr. Bob & his great info. post, I've done a more comprehensive writeup on the job of removal & replacement of the front valve, including pictures, tool suggestions, and some timesaving tips. Up to this point, I've been taking advantage of the time & effort that so many have put into their articles & posts, that I wanted to reciprocate by sharing my experiences & shortcuts for this particular job.
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