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THERMISTOR CURVE
90
80
70
60
50
40
30
20
10
0
0
20
40
TEMPERATURE (DEG. F)
Fig. 41—Resistance Values Versus Temperature
then off, the signal will remain off for 4 sec before turning on again
to start the next cycle. The PWM is called a 20–percent duty-cycle
signal. If the on time is increased to 4 sec of the 5 sec period, the
PWM is called an 80–percent duty-cycle signal. The ICM reads the
PWM signal and increases the motor speed linearly from minimum
speed to maximum speed with the percent duty-cycle value of the
supplied PWM signal.
EMI FILTER
An electromagnetic-interference (EMI) filter is installed on the
high-voltage input to the ICM to prevent electromagnetic signals
generated by the ICM from interfering with other home appliances,
such as radios or televisions.
Step 5—LED Function/Malfunction Lights
The
2-speed
control
is
function/malfunction light.
NOTE: Only malfunction signal appears at thermostat. Both
function and malfunction signals appear at control board. (See Fig.
35 for LED location.) Table 16 provides the function/malfunction
code, location, and definition.
Step 6—Troubleshooting
NOTE: Troubleshooting charts for air conditioning and heat
pump units are provided in the back of this manual — see Fig. 54,
55, and 56.
COMPRESSOR WINDING CHECK
The 2-speed compressor is nothing more than 2 single-phase
motors within 1 compressor shell. When the compressor fails to
start or run, there are 3 tests that can be made: open, ground, or
short. This compressor has no internal line-break overload; how-
ever, it does have PTC motor protectors. See Compressor PTC-
Overload Protection section for PTC overload information.
NOTE: To ensure accurate ohm measurements, place ohmmeter
probes on flat surface of compressor-terminal tabs, not the brass
mounting screw.
Open
To determine if a winding has an actual break in the internal wires
and current is unable to pass through:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals T1, T2, T3, T7, and T8.
60
80
100
120
A91431
equipped
with
an
LED
4. Use an ohmmeter on 0-1000 ohm scale to check resistance.
(See Fig. 40, 42, and 43 and Table 19.)
Because winding resistances are usually less than 10 ohm, each
reading will appear to be approximately zero ohm. If during any
check the resistance remains at 1000 ohm, an open or break exists,
and the motor or compressor should be replaced.
Ground
To determine if any wire has broken and come in direct contact
with the housing or shell, causing a direct short to ground:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from T1, T2, T3, T7, and T8.
4. Allow crankcase heater to remain on for several hrs before
checking motor to ensure that windings are not saturated with
refrigerant.
5. Using an ohmmeter on R X 10,000 ohm scale, place 1 meter
probe on ground motor or compressor frame. Make a good
metal-to-metal contact. Place other probe on terminals T1, T2,
T3, T7, and T8 in sequence. Note meter scale.
If any reading of zero or low resistance is obtained, the motor is
grounding. Replace the compressor.
Short
This is an extremely critical test and is not advised unless the
following conditions are met.
The correct motor-winding resistances must be known before
testing. See Table 19 for cold-motor winding resistance.
The temperature of the windings must be specified, 70°F ± 2°F.
The resistance-measuring instrument must have an accurate ohm-
meter (such as a Wheatstone bridge or null balance-type instru-
ment).
The motor must be dry or free from direct contact with liquid
refrigerant.
To determine if any wires have broken through their insulation and
come in direct contact with each other, thereby shorting all or
part of the winding(s):
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals T1, T2, T3, T7, and T8.
4. Subtract instrument probe and lead resistance from each
reading. If any reading is within ± 20 percent of the known
resistance from Table 19, the motor probably does not have a
short. Usually a considerable difference will be noted if a
turn-to-turn short is present.
CONTROL-BOARD FAILURE
The control board continuously monitors its own operation and the
operation of the system. The diagnostic feature allows easy
troubleshooting of the control and system in the field. If a failure
occurs, the LED light on the control will flash a failure code. If the
failure is internal to the control board, the light will stay on
continuously (no flash). Before replacing control board, reset the
24v power. If the fault clears, check to ensure the indoor and
outdoor unit and electrical service are properly grounded. If the
entire system is grounded, the control board should be replaced, as
the control is not field reparable. If the control-board light is
flashing, see LED and Table 16 for function/malfunction defini-
tion. Cycling 24 vac to control board resets previous error
messages and any lockouts which have occurred. See Table 20 for
more information regarding control-board operation.
36
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Table of Contents
Troubleshooting
