First, I do know this is an old post, and I certainly understand that the opinions of those that answered the OP opt for taking it to a specialist.....

But, we can't all afford to run to the dealer every time we have an issue without at least looking for some of the things that we can fix....

My AC compressor does not come on so I tried looking at the obvious things like the fuse and the diode for the compressor. Since I have 2 HHRs, I took the diode out of one and swapped with the other without any change in results.
When I turn on the AC switch the light on the button does come on, but the compressor does not run, nor does the radiator fan come on.
My question is, are there other areas, that I can check before I take it to a professional?
If the Freon is low, is there something that shuts down the compressor?
I just want to figure out what kind of bill I am looking at if I can't find something stupid that I can fix.

If it is just low on freon, are those "kits" with the gauge really that bad to use if you follow the instructions?

 

I would try a recharge kit just to be sure, then if that fails take it in to a pro shop for a leak test

 

If you are low on refrigerant, you have a leak somewhere. You will ultimately have to find out where the leak is. Adding refrigerant would only be a temporary fix. The average person doesn't have the proper equipment (or knowledge) to diagnose and/or repair air conditioning systems at home. Sometimes you just have to take it to the shop.

 

To answer your question, yes there is a low pressure cut out that will shut down the compressor if the freon is low.

 

I once took an automotive cooling system class. It lasted all of three hours at the local vocational school, but I got a certificate to hang on the wall and that was good enough for my boss.

We did not have a freon recovery system at all. I took the compressor out of an old freezer to use for a vacuum pump and I bought a used set of Miller air conditioning gauges and hoses at the community sale for next to nothing. The hoses were crap and probably cost me as much to replace as a whole new manifold set would have but I was young and had the money at the time. They paid for themselves in no time anyway. About 5 years ago I bought a set of adapter ends for the hoses so I can do the R134a systems now.

They were fine for automotive use and also worked fine for HVAC although I have never messed with central air much except for one apartment I rented for a short while.

The building owner had a tank of the correct freon in his shed but had no hoses to put it in with. Once topped up the central worked fine all summer. I moved out when winter came so I don't know if it worked again the next year or not.

A while back I checked into getting a freon recovery system but boy are those costly. I can pull a vacuum on a system with my old freezer compressor, once that is done all it takes is time to see if the gauges have moved or not. If they have not there are probably no leaks so I can just fill it up again. I've often worried that there may be to much oil in the system but so far none of the cars I've done this on have failed for lack of or too much oil.

Most of the vehicles I've done were either family members or my own. I've done a few for friends but I always try to talk them into taking it to a certified shop first. When the air quit working in our '90 Mazda it had had R12 in it I think, whatever it was you couldn't get it anymore unless you were licensed.

I bought the conversion kit to change it to R134a but had no way to catch the old freon so I just sorta let it out into the atmosphere. I tried to hook up the vacuum pump to the low pressure side and catch the freon in an empty R22 canister I had collected somewhere but it just did not work. Maybe I should have tried the high pressure side ?

As the freon left the system I'm pretty sure it took all the oil that had been in the system with it. The recharge kit I had bought had a little tube of air conditioner oil in it so I put that in along with the freon. I also added one can of R134a that had a leak detector fluid in it but never did find a leak in the system.

I ran the car for another 4 years and the air never faltered in all that time. I ran the air the day I drove it to the junkyard.

 

Back in the late 70's, early 80's of my mechanic days, AC work was probably about a 1/3 of my workload.
We would just bleed down a system into the atmosphere.
I'm sure I have my own personal little hole in the ozone layer.

 

It is OK to bleed to atmo IF it filters through a soaked rag. Then it turns to liquid. Or so my A/C guy told me when I asked him why he was doing it that way.

 

That was only one of the questions he asked. He also asked Yes there are but you really need to have the proper tools to diagnose it and Which I also answered in my other post. As far as a 'low pressure cut out' actually, the HHR has a AC refrigerant pressure sensor that will shut down the the compressor if the pressure is either too low or too high.

 

That would be what is commonly referred to as a crock......

 

I actually have two recovery machines. A Central Machinery Recovery/Recharge that I use exclusively for R134a, and an old White Industries 1060 that I use for R12, R12 alternatives and home HVAC. The old one is easy to change containers in and clean out to avoid contamination from mixing refrigerants. I haven't released refrigerants into the atmosphere since I received my HVAC/MVAC licenses back in the 90s. They're fairly easy to get as Grizzly alluded to but fairly difficult to have reinstated. And there's the fine that goes with it also if you get caught (up to $25K)......