First, many thanks to Volvodad (last summer) and Spook (last week) for their kind assistance to date.

On 92 940GL 196K,

1. MCC power switch failed a couple of years ago
2. Local garage installed toggle switch taking power from a post underneath fuse 16 and connecting (soldered) directly to the Green/Red wire prior to the "plastic coupler" in the line just before it enters the compressor - this worked fine for running the AC (thusly wired, the toggle switch activates the compressor whether the fan is running or not and it appears in my uneducated view that the low and high pressure swithces or any other of the standard AC circuitry do not come into play either when the toggle is used)
3. Last spring, following instructions in FAQ, I "reflowed" a cracked joint (one joint only - others appeared sound) on MCC circuit board and this restored the MCC power switch function
4. A "couple of months" later - Fuse 16 began to blow anywhere from a few seconds to a minute or so after the AC was turned on. The fuse blew whether the MCC power switch was used OR the toggle switch (with or without the fan on). However, as long as the compressor ran, it blew cold air.
5. When warm weather arrived this spring, the MCC power switch no longer functioned and the fuse continues to blow as before when using the toggle switch. Again, cold air delivered as until the fuse blows.
6. Last evening, with voltmeter in hand, the following was found:
a. With toggle switch on - 9V at compressor = compressor runs/fuse blows
b. At the Low Pressure Switch connector:
1. Toggle OFF and MCC OFF - Pin A 12V Pin B No voltage
2. Toggle ON and MCC OFF - Pin A No voltage Pin B 9V
3. Toggle OFF and MCC ON - Pin A 9V Pin B No voltage
c. In addition when MCC is turned ON (toggle OFF), a faint click is heard from the control unit after approximately 2 seconds (which in my uneducated view might be the sound of the MCC relay contacts) but the compressor still doesn't run.
7. Next, per Spook's post last week, I "hot wired" 12 volts to the low pressure switch and the compressor ran and blew cold air. Per Spook, this implies the compressor is good and is an indictment of the MCC circuitry. I did notice the wire I used became extremely hot after 2-3 minutes. I don't know what size wire or whether this observation is significant but it was a multistrand wired that came from a ceiling fan light kit.
8. Again, per Spook's post, I then removed the MCC and attempted to "reflow" the solder around 2 pins on main connector and two pins on the relay. One of the relay pins was troublesome - wanted to flow UP the pin instead of down to the pad and didn't look "pretty" when I finally gave up on it. (So if this doesn't work, I am not sure whether it is because of failure of the relay or failure of my soldering skills.)
9. This morning I reinstalled the MCC and the power switch still does function - although I continue to hear the faint click referred to in 6.C above.

So, after all that, I am wondering, is the compressor bad? Is the MCC definately fried? Are both true?

1. As wired, does the toggle switch bypass all other circuitry? If so, does this mean the compressor is the source of drawing too much current and blowing the fuse? If so, does that mean the compressor is bad or is there some other possible explanation related to the compressor? External wiring (what's in those in-line plastic couplers anyway?)? How does one troubleshoot that?
2. Are my questions about the compressor actually irrelevent (thus showing my extreme ignorance)and therefore the MCC must be the source of the problem? If so, is there a reasonably easy way to check the function of the individual solder joints. Is there a way to check the function of the relay?
3. And, finally, if I just skip over all this and "borrow" a known good MCC from a "friendly source" for further troubleshooting OR purchase one since this one appears fried, is there a possibility that if the compressor is also bad or something else outside the MCC circuit board is causing the problem - that it will damage the replacement MCC?. ( I assume that's why there's a fuse there - to protect it, but this is not territory I am comfortable with as far as my knowledge is concerned).

For those with the patience to stick with me, thanks. I tried to be as succinct is possible but I realize I am a "tad" obsessive. I also realize I frequently tend to make things more complicated than they really need to be - I hope that's the case here!. I will look forward to your responses.

Gratefully,

Calvin
92 940 196K
96 850 Turbo 96K