Carrier 38TN Service Manual page 7

HN67ZA008
Fig. 8—Cycle Protector Device
Y YEL
TERMINAL
BOARD
CONNECTION
Step 6—Crankcase Heater
Crankcase heater is a device for keeping compressor oil warm. By
keeping oil warm, refrigerant does not migrate to and condense in
compressor shell when the compressor is off. This prevents
flooded starts which can damage compressor.
On units that have a single-pole contactor, the crankcase heater is
wired in parallel with the contactor contacts and in series with the
compressor. (See Fig. 11.) When the contacts open, a circuit is
completed from the line side of the contactor, through the
crankcase heater, through the run windings of the compressor, and
to the other side of the line. When the contacts are closed, there is
no circuit through the crankcase heater because both leads are
connected to the same side of the line. This allows the heater to
operate when the system is not calling for cooling. The heater
does not operate when the system is calling for cooling.
The crankcase heater is powered by high-voltage power of unit.
Use extreme caution troubleshooting this device with power on.
The easiest method of troubleshooting is to apply voltmeter across
crankcase heater leads to see if heater has power. Do not touch
heater. Carefully feel area around crankcase heater. If warm,
crankcase heater is probably functioning. Do not rely on this
method as absolute evidence heater is functioning. If compressor
has been running, the area will still be warm.
T2
T1
T3
CUT YELLOW WIRE
BETWEEN CONTACTOR AND
LOW-PRESSURE SWITCH
SAFETY
YEL
CONTROL
YEL
T1
Fig. 10—Cycle Protector Wiring
3
SEC
T1
_
T2
BLK DENOTES CLOSED CONTACTS
A94005
Fig. 9—Cycle Protector Sequence
YEL
VIO
LOGIC T3
T2
Fig. 11—Wiring for Single-Pole Contactor
With power off and heater leads disconnected, check across leads
with ohmmeter. Do not look for a specific resistance reading.
Check for resistance or an open circuit. Change heater if an open
circuit is detected.
Step 7—Time-Delay Relay (TDR)
The TDR is a solid-state controlled recycle delay timer which
keeps the indoor blower operating for 90 sec after thermostat is
satisfied. This delay enables the blower to remove residual cooling
in the coil after compression shutdown, thereby improving the
efficiency of the system. The sequence of operation is that on
closure of the wall thermostat and at the end of a fixed on delay of
7
OPERATING
5 MIN
TIME
HN67ZA008
C BRN C
TERMINAL
BOARD
CONNECTION
BLK
CH
11 21
A94009
A88415
A94008