GVZC20 Service Manual
SERVICING
17
NOTE: If an open compressor is indicated, allow ample
time for the internal overload to reset before replacing com-
pressor.
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.
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 an ohmmeter on the R x
10,000 scale or the highest resistance scale on your
ohmmeter check the resistance between each of the
three leads separately to ground (such as an unpainted
tube on the compressor).
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.
5. Carefully retest for ground, directly between compressor
terminals and ground.
6. If ground is indicated, replace the compressor. The resis-
tance reading should be innity. If there is any reading
on meter, there is some continuity to ground and com-
pressor should be considered defective.
OL
The crankcase heater must be energized a minimum of 2
hours before the unit is operated. Crankcase heaters are
used to prevent migration or accumulation of refrigerant in
the compressor crankcase during the o cycles and pre-
vents liquid slugging or oil pumping on start up. A crankcase
heater will not prevent compressor damage due to a ood-
back or over charge condition.
1. Disconnect the heater lead in wires.
2. Using an ohmmeter, check heater continuity - should
test continuous. If not, replace.
NOTE: The positive temperature coecient crankcase
heater is a 33 watt 240 voltage heater. The cool resistance
of the heater will be approximately 1745 ohms. The resis-
tance will become greater as the temperature of the com-
pressor shell increases.
The *VZC20 outdoor units and AVPEC* indoor units are fac-
tory equipped with:
• (Ta) an outdoor air temperature sensor
• (Tm) an outdoor coil temperature sensor
• (TI) an outdoor liquid temperature sensor
• (Td) a discharge temperature sensor
• (Tb) a defrost temperature sensor
• (Tgi) an indoor gas temperature sensor
• (Tli) an indoor liquid temperature sensor
To check above sensors:
1. Disconnect power to the heat pump condensor.
2. Disconnect the sensor from the electric board.
3. Connect an ohmmeter across the sensor terminals. The
ohmmeter should read be the resistance shown in the
table THERMISTOR RESISTANCE AND TEMPERA-
TURE CHARACTERISTICS. Replace the sensor if the
sensor is open, shorted, or outside the valid resistance
range.