Allis-Chalmers 7020 Tractor Air Conditioning Overhaul "Disaster", Part 1

Here's a mediocre video about an air conditioning system rebuild project on an Allis Chalmers 7020 model tractor that started out fine, soon began to go poorly and may be going better now. I'm not a Super Tech(tm), nor have I ever claimed to be.

The moral of this story is "don't take shortcuts". Expecting the factory installed thermostatic expansion valve (TXV) to be good was definitely a mistake. Chalking up the lousy vacuum (about 5,000 microns at best) to the age of the system was also a mistake. There will be a second part to this video. Replacing the seals and TXV up in the evaporator compartment also turned into a frustrating experience (which you will see in part 2).

0:00 - A look at the project after the old compressor was removed.
1:20 - Leak test results (done with trace refrigerant gas) on the original system.
1:40 - The old compressor (GM/Delco Air A6).
2:08 - New Sanden compressor/conversion kit from AP Air.
2:27 - Assessment of the system seals. (All since replaced.)
2:44 - Nitrogen flush of individual parts, removal of old mineral oil.
3:45 - Famous last words!
4:08 - BE NICE! (I mean it!)
4:45 - New compressor mounted.
5:06 - I didn't actually take the Schrader cores out. Forget I said that. Aging is all in the mind, and that's the first thing to go.
6:10 - Nitrogen pressure/leak testing.
7:10 - Listening carefully for leaks.
9:00 - Compressor/control electrical checks (do the in-cab controls actually work? Why is my father so easily amused by a fan?) ...
11:19 - Close up look at the new compressor mounting and adapters.
11:50 - Tales of a new idler pulley and escaping belt.
12:54 - My father, very excited about cleaning up mouse nests.
13:04 - Flushing solution after a trip through the evaporator coil.
13:08 - Did the system pass the nitrogen leak test?
15:22 - First vacuum pump run.
15:31 - Schrader valve core strife.
17:35 - Picture of the (damaged, by that point) Schrader valve core that refused to come out.
We finally pulled the hose and drilled it out, as there is no need to put a new valve core in the original service fitting, since it will have an R-134a service adapter fitted.
17:40 - Vacuum (micron) gauge readings, of which I forgot to get enough pictures...it did go into deeper vacuum than what is shown.
17:56 - Refrigerant charging attempt.
20:50 - Starting the A/C system up.
21:26 - Checking the sight glass.
21:33 - Theorizing about what went wrong. (See notes in description.)

Postscripts:
24:11 - Leaky gauge set, stolen refrigerant drum, Acme fittings.
25:00 - Bad refrigerant scale.
27:00 - Keykeeper appearance!
27:25 - Keykeeper agrees, something's wrong.
28:19 - Refrigerant recovery.
29:34 - Mouse mess.
29:53 - Almost lost the service caps!

I am going to have to send my Stride/Imperial gauges in for service, because they are definitely not vacuum tight. The system was trying to work with the original TXV. The evaporator coil even managed to sweat a little bit. We had a very poor temperature differential. It's here that I'll admit I'm not entirely sure of what was happening as discussed at 21:33. Since the compressor was trying to pull into a vacuum and the low pressure switch was cutting it off, I thought the TXV was stuck shut and the evaporator being starved of refrigerant. I'm not sure -- the suction line was not cold. I can't imagine the evaporator was flooded based on that, but maybe? Constructive thoughts welcomed, especially if you worked on one of these when this tractor was new.

What is the intended purpose of the "purge" (seems like a medium in-cab fan speed) setting?

As promised, here's a little about the back story of this tractor. My father bought it used. At the same time, another person also bought another tractor from the same dealer. They soon found out that both tractors had basically been assembled from all sorts of different parts. Not too long after that, the other tractor was stolen in broad daylight. People actually saw a truck and trailer show up, but nobody questioned them because it really didn't seem like an unusual thing for someone to be moving a tractor. This leads up to the scam being run by the dealer: they'd sell the tractor, lay low for a while, steal it when nobody was around and sell it again. (Tractors in this part of the world aren't generally licensed and titled like a car or truck would be.) Not long after that, police in the area became aware of what that tractor dealer was doing. I don't know if anyone has been arrested or the operation closed down. After the other tractor was stolen, this one was hidden. As best we can tell, this Allis Chalmers tractor had yet to be stolen and resold, what with its having been freshly "assembled" prior to being ready for sale.

I'm not kidding when I say "be nice" to both myself and others.