Service Manual

SERVICING
41
NOTE: If an open compressor is indicated, allow ample time
for the internal overload to reset before replacing compressor.
S-17B GROUND TEST
If fuse, circuit breaker, ground fault protective device, etc.,
has tripped, this is a strong indication that an electrical
problem exists and must be found and corrected. The circuit
protective device rating must be checked, and its maximum
rating should coincide with that marked on the equipment
nameplate.
With the terminal protective cover in place, it is acceptable to
replace the fuse or reset the circuit breaker
ONE TIME ONLY
to see if it was just a nuisance opening. If it opens again,
DO
NOT continue to reset.
WARNING
Disconnect ALL power before servicing.
Disconnect all power to unit, making sure that all power
legs are open.
1. DO NOT remove protective terminal cover. Disconnect
the three leads going to the compressor terminals at the
nearest point to the compressor.
2. Identify the leads and using a Megger, Hi-Potential
Ground Tester, or other suitable instrument which puts
out a voltage between 300 and 1500 volts, check for a
ground separately between each of the three leads and
ground (such as an unpainted tube on the compressor).
Do not use a low voltage output instrument such as a volt-
ohmmeter.
HI-POT
COMPRESSOR GROUND TEST
3. If a ground is indicated, then carefully remove the com-
pressor terminal protective cover and inspect for loose
leads or insulation breaks in the lead wires.
4. If no visual problems indicated, carefully remove the leads
at the compressor terminals.
WARNING
Damage can occur to the glass embedded terminals if
the leads are not properly removed. This can result in
terminal and hot oil discharging.
Carefully retest for ground, directly between compressor
terminals and ground.
5. If ground is indicated, replace the compressor.
S-17C UNLOADER TEST PROCEDURE
(2 STAGE COMPRESSORS ONLY)
A nominal 24-volt direct current coil activates the internal
unloader solenoid. The input control circuit voltage must be
18 to 28 volt ac. The coil power requirement is 5 VA. The
external electrical connection is made with a molded plug
assembly. This plug contains a full wave rectifier to supply
direct current to the unloader coil.
UNLOADER SOLENOID
(Molded Plug)
Unloader Test Procedure
If it is suspected that the unloader is not working, the following
methods may be used to verify operation.
1. Operate the system and measure compressor current.
Cycle the unloader ON and OFF at 10 second intervals.
The compressor amperage should go up or down at least
25 percent.
2. If step one does not give the expected results, shut unit
off. Apply 18 to 28 volt ac to the unloader molded plug
leads and listen for a click as the solenoid pulls in.
Remove power and listen for another click as the unloader
returns to its original position.
3. If clicks can’t be heard, shut off power and remove the
control circuit molded plug from the compressor and
measure the unloader coil resistance. The resistance
should be approximately 350 ohms or approximateley
1640 ohms.