content_image/568305.jpg content_image/568307.jpg content_image/568306.jpg content_image/568308.jpg
<img src='content_image/568305.jpg'>

<img src='content_image/568307.jpg'>

functioning normally fully condenses all the refrigerant flowing through the condenser. 

## Service Valves 

All vapor cycle air conditioning systems are closed systems; however, access is required for servicing. This is accomplished through the use of two service valves. One valve is located in the high side of the system and the other in the low side. A common type of valve used on vapor cycle systems that operate with R12 refrigerant is the Schrader valve. It is similar to the valve used to inflate tires. [Figure 16-84]  A central valve core seats and unseats by depressing a stem attached to it. A pin in the servicing hose fitting is designed to do this when screwed onto the valve’s exterior threads. All aircraft service valves should be capped when not in use. 

<img src='content_image/568306.jpg'>

R134a systems use valves that are very similar to the Schrader valve in function, operation, and location. As a safety device to prevent inadvertent mixing of refrigerants, R134a valve fittings are different from Schrader valve fittings and do not attach to Schrader valve threads. The R134a valve fittings are a quick-disconnect type. 

Another type of valve called a compressor isolation valve is used on some aircraft. It serves two purposes. Like 

<img src='content_image/568308.jpg'>

