Hi Johnson -
Since noone has answered your original question, I'll give
it a shot.
The expansion valve is under the hood on the 124, right
at the rearmost firewall. It is next to the power brake
booster, toward the center of the car. It's quite easy to
see, though working on it would be a different issue...
In simple, non-technical terms: Find the brake master
cylinder. The booster is the big pie-plate thing to which
the master cylinder is mounted. Look toward the center of
the car and down a bit. The expansion valve is a block
of metal about 2"x2" square, and perhaps 1" thick. It has
two metal lines going through the firewall into the
interior of the car, and two lines connected to the
opposite side which head toward the front of the car.
The two lines heading into the inside of the car are in
fact the inlet/outlet of the dreaded evaporator. The other
two are the high side/low side lines to the compressor.