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166240004
12/1/94
Rev 3/4/96
SERVICE STEM VALVES
When closing the service stem valves to remove your gauge and manifold set always close the high side stem
valve first. Following this procedure will allow the system to “PULL” the refrigerant vapor from your manifold set
to reduce refrigerant loss. When the pressure has been reduced, close the low side stem valve.
MOISTURE CONTAMINATION
With the major changes in refrigerants in today’s marketplace and the use of hydroscopic oils the control of
moisture and contaminates have become more critical to safeguard against than ever before in the history of
mechanical refrigeration.
Contaminates are also the most difficult of all problems to determine. A Meg-Ohm meter “Megger” can be a
valuable tool to aid in the analysis of this problem. A Meg-Ohm reading log may be started any time after 90
days of operation of the product. To perform the test, proceed as listed.
Disconnect all three (3) compressor leads, take a Meg-Ohm meter reading from each compressor terminal to a
good chassis ground. Compare reading to chart below:
Meter Reading
MegĆOhm
Compressor Condition Maintenance Required
100 Ć ∞
Okay None needed.
50 to 100 Moisture present Replace drier.
20 to 50 Severe moisture & possible contaminated oil
with acid present
Replace drier with acid hold type. Run 24
hours, change to regular drier.
.5 to 20 System has severe contamination Remove compressor oil and refrigerant charge.
Evacuate, install liquid and suction line driers
(acid hold type). Recharge with new oil and reĆ
frigerant. Run 24 hours. Discharge system, disĆ
card suction line drier, replace the liquid line
drier. Evacuate and recharge.
Readings in the range listed below 100 Meg-Ohm would be an indicator that the system being tested may have
a contamination problem. Where does the problem come from? As an example, the filter drier may become sat-
urated and hold large percentages of moisture and the system function without a problem until such time as the
product operating conditions change. Should the room temperature increase, or the condenser plug-up etc., the
higher operating pressures and temperatures may cause the drier filter to release a portion of it’s held moisture.
It is also imperative to avoid opening the sealed refrigeration system whenever possible and when it is done to
be certain the true problem is correctly diagnosed and repaired. Remember, service gauge sets should only be
installed after all external checks have been performed.
CAUTION: Megger checks should NEVER be performed on any compressor that is under a
vacuum.
COMPRESSOR CONTACTOR
The contactor serves as the voltage supply switch for the compressor circuit. Voltage to the coil of the contactor
is supplied by the circuit board.
Check Out:
The two (2)* line supply screws of the contactor should always have supply voltage present when voltage is on
to the product.
The other two (2)* screws (load) should have line voltage when the contactor is energized. The contactor coil
receives its supply voltage from the circuit board. Should the contactor fail to energize: