Does anyone know what the purpose of the little valves are that are in the few brass fittings on the high pressure line that runs from the expansion valve to the drier/receiver?

One of the O-rings on them is torn and they don't look like any of the o-rings that came in the system kit.

 

Picture ? O rings in valves don't sound right...

 

Depending on the year of the vehicle, the A/C system will either have an High Pressure Switch or a Thermostatic Expansion Valve. The purpose of these "valves" is to help control the refrigerant (R12 or R134a) circulation and also as a "switch" to cycle the compressor on or off. The TXV is used on older systems while the High Pressure Switch is on newer systems. Sounds to me like you are discribing an Orifice Tube which is an inline filter in your A/C or some systems have "crush washers" as gaskets for the fittings. A few pics of your parts might better help us to point you in the right direction. Hope this helps. Good luck.

 

Mine is a 93 with the expansion valve.

This assembly is on the expansion valve side of the receiver/drier.



Where do I get o-rings for this?

 

There just ac fitting O-rings autozone sell a small kit...http://shop.advanceautoparts.com/web...erm=ac+o-rings