EngA C-TRAC2 Installation, Operation And Maintenance Manual page 34

A
Determine type of compressor – Hermetic (welded) or Semi-Hermetic (bolted)
1. Hermetic Compressors
 Most hermetically sealed compressors have internal pressure relief valves. If so equipped, there is usually no
external high-pressure switch (usually open above 360#).
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Some hermetic compressors have compressor protection modules.
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Some hermetic compressors have auto reset low pressure switches (open 20#, close 65#).
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Very few hermetic compressors have oil pressure switches.
2. Semi-Hermetic Compressors
 All semi-hermetic compressors have high, low, and oil pressure switches that operate at pressures noted in 1
above.
3. Compressor Protection Modules
 Some compressors have compressor protection modules (CPM), many CPM's have internal anti-cycle 3-minute
timers.
4. If compressor doesn't run:
A. Ensure there is power to contactor coil:
 If not, check above-noted switches to ensure they are not tripped.
 Check system for refrigerant gas.
B. If contactor coil has power and contactor is pulled in, but compressor doesn't run;
 Does power pass through contacts of contactor?
 Is power at compressor terminals?
 If power is present 
 Extra Controls Which May be on Unit
Condenser Fans
Some run constantly with any call for cooling. Others cycle to maintain head pressure. (Stage 1 on/off, 240/180
normal max.; Stage 2 on/off, 260/200 normal max.)
Hot Gas Bypass
.
Opens as load falls Should begin opening about 63#, fully open 53#.
Cylinder Unloading
To reduce compressor capacity unload below 67#. Return to full capacity about 77# suction.
Semi-Hermetic Compressor
 Turn off power, measure motor winding resistance leg to leg and
leg to ground. If open circuit or shorted – replace compressor.

Hermetic Compressor
 Turn off power, measure winding resistance leg to leg and leg to
ground. If open circuited and compressor shell is hot – disconnect
power, leave for 24 hours and recheck when cool. (Why? Internal
line break protection may open circuit when hot). If shorted –
replace compressor.
C-TRAC2.1 MANUAL
Page x March 1999 R1