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MODE OF OPERATION
18-PIN CONNECTOR
All
Low-speed Cooling
High-speed Cooling
Low-speed Heating
High-speed Heating
Defrost
Second Stage of
Auxiliary Heat
Cooling Second-
stage Latching
CONTROL-BOARD POWER INPUTS AND OUTPUTS
See Fig. 35 and 39 for inputs and outputs.
BLEED RESISTOR
The bleed resistor is a 150k, 2–watt resistor across the compressor-
run capacitor to protect service technician from injury by electrical
shock. Capacitor will bleed-off approximately 1 minute after
power to outdoor unit is turned off. If run capacitor is changed out,
be sure to place bleed resistor on new capacitor. If bleed resistor is
damaged, replace resistor.
START CAPACITOR AND RELAY
The 2-speed system has a second start relay in the control box. One
start relay is for low-speed start, and the second is for high-speed
start. Both start relays use a common start capacitor. When
servicing this equipment, be certain system starts in both low- and
high-speed operation.
INTEGRAL-CONTROL MOTOR (ICM)
If the outdoor fan motor fails to start and run, first check the
high-voltage supply. The unit need not be running to check high
voltage, but the power must be on. With a voltmeter, check for
230vac on the brn and blk motor leads at the EMI filter, if
installed. If the 230vac is not present, check the supply and the
EMI filter for faulty connections, faulty wiring, or faulty EMI
filter. Repair or replace as necessary.
If the 230vac is present, use a voltmeter on a DC voltage scale to
check the control-line voltage to the fan motor. At full fan-motor
speed, the voltmeter should indicate 20-40vdc with the motor
disconnected and 16-20vdc with the motor connected. The fan
motor runs at full speed whenever the outdoor temperature is
greater than 90°F or when the compressor is at high speed
(cooling), and less than 22°F (heating). The voltage reading will be
lower at temperatures in between.
First check voltage with the motor disconnected. If no control
voltage is present, check control-board connections. If connections
are good, replace the control board.
If voltage is present, reconnect the motor and check again. Shut
down the unit to reconnect the motor and restart the unit to
complete this troubleshooting procedure. If control voltage is no
longer present or motor fails to respond, check motor connections.
If connections are good, replace the motor.
REFRIGERATION SYSTEM
Step 1—Refrigeration Cycle
In a refrigeration system, refrigerant moves heat from one place to
another. It is useful to understand flow of refrigerant in a system.
Table 20—24v Pin Connection Troubleshooting
TERMINAL
LOCATION ON
DESIGNATION
CONTROL BOARD
R-C
2-1
Y1,0-C
8,6-1
Y1, Y2, 0-C
8,7,6-1
Y1-C
8-1
Y1-C
8-1
Y2-C
7-1
Y1-C
8-1
Y2, W2, 0-C
7,5,6-1
Y1, W2-C
7,5-1
W3, Y2-C
9,8-1
Y1, Y2, 0-C
8,7,6-1
VOLTAGE
VOLTAGE
PATH
REQUIRED
Input
24
Input
24
Input
24
Input
24
Input
24
Output
24
Input
24
Output
24
Input
24
Output
24
Input
24
In a straight cooling system, compressed hot gas leaves compres-
sor and enters condensing coil. As gas passes through condenser
coil, it rejects heat and condenses into liquid. The liquid leaves
condensing unit through liquid line and enters metering device at
indoor coil. As it passes through metering device, it becomes a
gas-liquid mixture. As it passes through indoor coil, it absorbs heat
and refrigerant and is again compressed to a hot gas. The cycle
then repeats.
In a heat pump, the basic cycle is the same. (See Fig. 44.)
Reversing valve in system decides which coil, indoor or outdoor,
becomes evaporator or condenser. It rejects heat into the home
after heat is absorbed by outdoor evaporator coil, thus the home is
heated.
In cooling cycle, the indoor coil becomes the evaporator. It absorbs
heat from the home and rejects it through the outdoor condenser
coil, thus the home is cooled.
A unique feature of the heat pump is that metering devices are
designed to meter refrigerant in one direction of flow and allow
refrigerant to pass unhindered in the other direction. If indoor-
metering device is metering refrigerant, the outdoor device by-
passes refrigerant and vice versa. This allows both coils to serve a
dual function.
Step 2—Leak Detection
Always wear safety glasses and gloves when handling refrig-
erants.
New installations should be checked for leaks prior to complete
charging.
If a system has lost all or most of its charge, system must be
pressurized again, up to approximately 150 lb minimum. This can
be done by adding refrigerant using normal charging procedures,
or it may be pressurized with nitrogen (less expensive than
refrigerant). Nitrogen also leaks faster than R-22 and is not
absorbed by refrigeration oil. Nitrogen cannot, however, be
detected by a leak detector. (See Fig. 45.)
Due to the high pressure of nitrogen, it should never be used
without a pressure regulator on the tank.
Leaks in a system pressurized with refrigerant can be spotted with
a leak detector which detects extremely small refrigerant leaks.
38
POSSIBLE SOURCE
OF PROBLEM
Check transformer (secondary)
Check thermostat
Check thermostat
Check thermostat
Check thermostat
Outdoor temperature below
speed; change temperature
Check thermostat
Outdoor temperature below 50°F;
Coil temperature less than 30°F
Check thermostat
Check balance-point setting
Ambient thermistor failure;
Check second-stage POT
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Troubleshooting
