You are reading the static pressure with the compressor not running. If it has been changed over to R-134 then pulling down to 35 PSI when it is 85 degrees means your system is low on freon. Fix this after the wiring issue.
You need to find out why you are not getting the cab wiring to power the AC clutch before addressing the freon issue. Your system basically works this way. The switch powers the cab relay which powers the accessories: Fan, radio, wipers, AC system etc. So if the accessories are working then the cab relay is working. Now you need to check if you are getting power to the AC thermostat control in the cab roof. IF you have power to it then turn it on and see if you have power out of it. ( I usually check this out with the top cab covers/roof off. I also clean everything out up there before I do any AC work. I have had many AC/heater issues be a dirty evaporator or heater cores.) If you have power coming form the AC thermostat then check the wiring to the AC compressor. The plug at the fire wall area is known to cause problems. You will need to do some investigating to get power to the AC clutch. Yours should also have the AC thermal over load fuse in the wiring by the compressor. The part # AR 77344 number 9 in the picture. This is to protect the compressor from running all of the time if low on freon. Some one may have removed it from your system. I would put it back in if you have the old style compressor. If it is a newer one some of them don't use the thermal fuse. Have to see what part number compressor you have to be sure.
Once you have the compressor running, a clean condenser core, a clean evaporator, plus a clean cab filter you are ready to top off your freon. You really need a set of gauges that shows both the high and low sides to really do this safely.
I usually just watch the low side as the compressor kicks in. I want it to not drop below 60-70 PSI if the temperture is above 70 degrees. The high side on R134 can be in the 300-350 PSI range on a hot humid day. I usaully just add freon until I get the low side to not drop more than I want it to. I then check the sight glass to see if I have any bubbles flowing. A few right at start up is OK. Some tractors You can't seem to get them totally bubble free. I go slow on the filling. I shut the compressor off and let it equalize the system equal out every now and then. Then watch the low side as it starts back up. I have found some tractors take more freon than the books says to really cool real good. That is why I rarely use the weight method to fill a system that is part way full.
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