Why Do We Have AN AC Pressure Switch

The switch opens both at a threshold low pressure and high pressure. I just replaced that switch (see this post: Air Conditioning Pressure Switch).

The high pressure cut-off is there in case the expansion valve gets plugged and the compressor just keeps raising the pressure.

As for why there is a low pressure cut-off, I am a little unclear too, although it means the system has lost refrigerant and is no longer holding pressure so there is no use in running the compressor.

 

Splash characteristics aside, it makes more sense for the system to be designed with the pressure switch present - so that it will work with *any* compatible compressor, not just the York. And as noted by Brian, high pressure in the system can be a problem no matter which compressor type.

 

Because the refrigerant also carries the oil for the compressor.

 

Correct: that's the reason

Ciao

 

None of this relates to your original question about the pressure switch, but oh well ...

While lubrication of the crank and pistons is through a splash system, other parts of the compressor are lubricated through oil circulating with the refrigerant. There is a small port which connects the crankcase to the upper part of the York compressor. This is process is described on the "Features" page of the York Service Manual (York Compressor Service Manual.pdf)

As noted in your Jedi.com link that you posted, a York compressor can be modified to be splash-only which is satisfactory for use as an air compressor because a little air leakage doesn't matter. The description of the modification in your link is: York Compressor Oil System Modification Page – Jedi.com (It is the link cited on your page in the bold face: "[ I’ll be updating this page eventually with updated info. Until then, check out the York oiling modification page. ]") Without that modification, oil escapes the crankcase as is also described in your links.

The measuring of the oil level using the dipstick should be done after the system has "stabilized" as described in the "Inspection" page of the Service Manual. "Stabilized" means after oil has distributed itself through the small port. The "stabilized" level should be at least 6 oz. And woe betide thee should ye openeth the oil fill plug when the system is pressurized.

I just completed refurbishing my system yesterday. (Among many other things) I flushed the entire system with Mastercool AC Flush Solvent, filled the compressor with 11.5 oz of Supercool Synthetic Ester Oil and recharged the system.