My Volvo is a 1989 model, so it has a rheostat as the method of controlling the air conditioner's condensor:

all the way counter-clockwise = off
border of red and blue = normal (full) power
all the way into the red = always on (but can leading to compressor freezing over)

(At least the above settings are how I understand the rheostat to work.)

I know that later cars (maybe 1991-1993?) came with a simple button in place of the dial. I assume the button functioned as the first and second options only--either off completely or running most of the time, shutting off when needed. There was no "full-on, overdrive" like with the rheostat.

Besides the fact that newer cars without "degree climate control" also seem to have only a button that turns on or off the compressor, I tend to use the air conditioner only with the compressor off or in the "normal" position--I don't use overdrive any more since it doesn't appear to help things get cooler, and it seems to lead to the air conditioning not cooling much at all after a while.

The point is, I think I would like to have a button in my car because the rheostat sometimes gets very difficult to shut off completely. Is it possible to swap out the rheostat with a later-style button with no modifications? In other words, if I disconnected the wiring from a button in a junkyard car, would I be able to put it directly into my car and have everything work? (The condensor functions predictably and the light--presumably--lights up at nighttime.)
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'89 244 GL -- 120,700 miles (see profile for info on car)