i assume you are talking about the tractor in your sig (B2650HSDC)
if that is the case, the evaporator has a temp probe that turns the compressor off if the evap temp drops below freezing. I have had to replace a few of those. Not much fun, but normally solves the problem--and you don't have to open the system for anything in order to replace the sensor
here is where people get into a pickle, by asking on a forum wher 'everyone' knows a/c systems (and only about 25% of them really do)
you're being told to check and/or replace parts that may not be needed; u need to isolate the cut-and-dried cause before you replace or service a single part. Adding a can or two is the wrong way to do it, you could potentially end up with an overcharge situation and never know it other than the system wont' cool when you need it to cool (like in the summer time
there is always a reason that a/c systems need repair. When I did dealer work, when I got a repair order, it usually said "a/c not working" and nothing more. So first thing to do is get a background. Call the customer personally and ask them the details. Did it just stop? slowly stop working over time? Any noises? Anyone add a can? Anyone else serviced it? Lots of times, even then I never got the whole story. And lots of times I found out that someone had been playing with it and it was over or under charged, compressor shot, air/moisture in it, even had a couple instances where the wrong refrigerant was used by inexperienced and untrained "techs" (and some of them were at other dealers). 99% of the time the condenser was plugged up or the belt was slipping but the ones that were not? Better get the whole story before even starting the engine, that or waste a bunch of time and money.
