Chapter 8 – Maintenance
TestEquity 1016S and 1027S Temperature Chamber
Page 8-7
The temperature controller alternately cycles the low-stage liquid-line solenoid valve (SV1) and
the hot-gas solenoid valve (SV2) ON/OFF through cool relay CR1 to control the chamber
temperature. When SV1 is ON, liquid refrigerant flows through the thermostatic expansion valve
and evaporator to cool the chamber. When SV1 is OFF, the flow stops. High pressure vapor
feeds the hot gas regulator through SV2, which meters a precise amount into the suction line to
maintain a minimum load on the system and keep it out of a vacuum. The hot gas regulator is
adjusted to keep the suction pressure at 2 PSIG when SV1 is OFF. Pilot Light PL2 provides an
indication on the front panel when SV1 is ON.
During a high temperature pulldown or a continuous bypass condition, it is possible for
excessive hot gas to return to the compressor. The suction line cooling thermostatic expansion
valve senses the suction line temperature and injects liquid refrigerant to cool the hot gas within
safe limits.
The receiver has an integral fusible relief which opens in the event of a fire. A high/low pressure
switch (DPS1) turns off the entire refrigeration system in the event of an out of limit condition.
The compressor is also protected by an internal overload device. The compressor has a crankcase
heater (CC1) to prevent refrigerant from condensing in the oil when the compressor is off.
The compressor rotation is phase-sensitive. A phase control relay (PCR1) ensures that the
chamber can operate only if the input power phase-sequence is correct.
The temperature controller has internal logic to turn the compressors on if cooling is required to
maintain the temperature set point.
