Chapter 8 – Maintenance
Page 8-8
TestEquity 1007S Temperature Chamber
The temperature controller cycles the low-stage liquid-line solenoid valve (SV1) 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, 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.
A high/low pressure switch turns off the entire refrigeration system in the event of an out of limit
condition. The compressor has a crankcase heater to prevent refrigerant from condensing in the
oil when the compressor is off.
The temperature controller has internal logic to turn the compressor on if cooling is required to
maintain the temperature set point.
