Bob's Studebaker Resource Website


Since service valves have not been in regular use for approximately 30 years, many certified A/C technicians have never worked on an air conditioning system that has service valves. Even technicians who have seen these older systems are out of practice, so let’s take a moment here to give some inside scoop on a compressor service valve system.

There are TWO valves on most York or Tecumseh compressors. One on the suction “low” side and one on the discharge “high” side of the compressor. (The system should always be charged on the SUCTION side.)

.... these rules apply to most York or Tecumseh style compressor from the mid 1950’s and into the early 1980’s, and some late 50’s to early 60’s Mopar products.

Once the system is ready to be charged, the valve must be adjusted to the CENTER seated position. (See figure 2) This position allows refrigerant to flow past the valves and through the service port. Set to this position, pressure gauge readings can be monitored and the system can be properly evacuated & charged. The best way to achieve the proper center seated position is to turn the valve clockwise until it stops in the front-seated position, then counterclockwise approximately 4 complete revolutions.

Once the system has been evacuated and properly charged, the valve should be back-seated for normal operating conditions. (See figure 3) This allows for full flow through the valves and blocks off the service valve port to prevent refrigerant loss. (A service valve cap is also used to further insure against leaks.) This setting is achieved by turning the valve counterclockwise until it stops.

A final tip and illustration related to these vintage A/C compressors; the valve should be slightly opened in a “cracked” position when checking system pressure readings. (See figure 4)