User Guide
11
The compressor capacity can be reduced by bypassing the hot discharge gas
through a solenoid directly to the suction line. A desuperheating valve must
be used in this type of system, to prevent the compressor from overheating
and tripping its internal protector.
As shown in Figure 10, an alternate approach is to feed the discharge gas to
the inlet of the evaporator. As the evaporator warms up, the thermostatic
expansion valve (TXV) will respond by allowing more flow, thereby acting
as a desuperheating valve. This approach is preferred, as it maintains good
velocity through the evaporator and prevents oil logging.
Hot-gas bypass
When defrost is required, the solenoid in the hot-gas-bypass system opens.
This allows discharge gas to go to the evaporator, thereby defrosting the coil
(see Figure 11).
A suction-stop solenoid is also needed in this system, to isolate the discharge
from going right back to the compressor.
Hot-gas defrost
Hot-Gas-Bypass Capacity Control
Figure 10
Hot-Gas Defrost
Figure 11