Carrier R-22 Application Manual And Service Manual page 35

FAILED COMPONENT
Ambient Thermistor
Outdoor Coil Thermistor
Furnace Interface Jumper
The 2-speed compressor contains motor windings that provide
low-speed, 4–pole (1750 rpm) and high-speed, 2–pole (3500 rpm)
operation. Refer to Fig. 40 to determine which windings are
energized at each speed. Refer to Compressor Winding-Check
section under Troubleshooting and Table 19 for appropriate
winding resistances.
The 2-speed compressor is also protected by an internal-pressure
relief (IPR), which relieves discharge gas into the compressor shell
(low side) when the differential between suction and discharge
pressures exceeds 500 psi. The compressor is also protected by 3
PTC devices attached to the motor windings. The PTC's resistance
is sensed by the 2-speed control board. See Table 17 for resistance
ranges.
MECHANICALLY INTERLOCKED CONTACTORS
T3 T8 T7 T2
EXTERNAL MAIN
MAIN WINDING
4 POLE START
2 POLE START
HIGH SPEED
(L1) T1 + T7
(L2) T2 + T3
Fig. 40—Energizing Windings
Table 18—Factory Defaults
FUNCTION
Crankcase Heater
Second-Stage Latching
Furnace Interface
Heating Switchover Speed Point
Defrost Initiation
Outdoor Thermostat for
Auxiliary Heat
Defrost Initiation and Termination
Furnace Interface
Table 19—Two-Speed Compressor (Winding Re-
The 2-speed products are equipped with mechanically interlocked
contactors. Each contactor has interconnecting linkage, providing
independent interlocks.
The 2-speed control provides the electrical interlock. The contac-
tors are supplied with 240-v coils, which reduce the va require-
ments of the low-voltage (24vac) control system.
TEMPERATURE THERMISTORS
T1
Thermistors are electronic devices which sense temperature. As
the temperature increases, the resistance decreases. Two ther-
mistors are used to sense temperature: one senses outdoor ambient,
and the other senses coil temperature (heat pump only). Refer to
Fig. 41 for resistance values versus temperature.
If the outdoor ambient thermistor should fail, a malfunction signal
appears on the indoor thermostat and 2-speed control. The control
does not initiate second-stage latching, crankcase heater is turned
on during all off-cycles, heating defaults to high speed, and defrost
initiates on demand from coil thermistor. (See Table 18.)
If the outdoor coil thermistor should fail, a malfunction signal
appears on the indoor thermostat and 2-speed control. The control
defrosts every 90 minutes of heating operation and terminates in 5
minutes. (See Table 15.)
ICM OUTDOOR FAN MOTOR
The outdoor integral-control motor (ICM) is a variable-speed
motor which operates from 400 to 900 rpm. The motor is a DC
permanent magnet-type motor with the electronic controls inte-
grated into its rear cover. The control package includes a small
diode bridge, capacitors, and power-switching devices. It converts
AC to DC power and switches the DC power to the motor
LOW SPEED
windings on and off at various rates to control the motor speed.
(L1) T1
The commutative speed of the motor windings is determined by a
(L2) T7 + T8
pulse-width modulated (PWM) signal which is received from the
control board on the motor-control lines.
A92015
The PWM signal is created by turning a DC signal on and off once
within a given period of time. The signal-on time relative to the
signal-total period defines the percent of the PWM. For example,
if the period is 5 sec and the control power is turned on for 1 sec
35
DEFAULT
Energized during any off cycle
Does not function
Balance point does not function, but
interface still energizes furnace and
locks out heat pump with a call for W2
Unit only runs in high-
compressor speed
Defrost is initiated based on coil
temperature only
Anytime there is a call for W2,
W3 is also energized.
Defrost occurs at each time interval,
but terminates after 5 minutes
Does not function
sistance at 70°F ± 2°)
WINDING 3 TON
T1-T2 0.80
T1-T3 3.20
T1-T7 1.30
T1-T8 3.10
4 TON 5 TON
0.70 0.60
2.20 1.80
1.00 1.00
2.20 2.00