Service Manual

56
ECM Fan Motor
Troubleshooting
If the outdoor fan motor fails to start and run:
S Check the high- voltage supply. The unit need not
be running to check high voltage, but the power
must be on.
S If the 230vac is present, use Table 15 to check for
proper control voltage output to the fan motor from
the control board. The control board sends DC
voltage signals to the motor through the terminals
labeled PWM1 and PWM2 Set a voltmeter on a DC
voltage scale and check across these terminals.
S 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.
S 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.
S If connections are good, replace the motor.
Time Delays
The unit time delays include:
S Five minute time delay to start cooling or heating
operation when there is a call from the thermostat
or wall control. To bypass this feature, momentarily
short and release Forced Defrost pins. Speed up is
also possible by pressing the Cool To or Heat To
button on the Communicating wall control.
S Five minute compressor re- cycle delay on return
from a brown- out condition.
S Two minute time delay to return to standby
operation from last valid communication (with
Communicating only).
S One minute time delay of outdoor fan at termination
of cooling mode when outdoor ambient is greater
than or equal to 100_F.
S Fifteen second delay at termination of defrost
before the auxiliary heat (W1) is de- energized.
S Twenty second delay at termination of defrost
before the outdoor fan is energized.
S Thirty second compressor delay when quiet shift
enabled.
S Seventy and sixty second compressor delays
when Quiet Shift- 2 is enabled.
S On *CH6 models there is a 1 minute time delay
between staging from low to high and from high to
low capacity. On *CH6 models there is no delay;
the compressor will change from low to high and
from high to low capacity “on the fly” to meet the
demand.
Pressure Switches
The R- 410A two- stage air conditioner contains two
pressure switches to prevent system operation if the
pressures get excessively high or low. The air conditioner
low pressure switch in the suction line opens at 50 PSI and
closes at 95 PSI. The high pressure switch opens at 670
PSI and closes at 470 PSI. Both pressure switch settings
are considerably higher than on comparably sized R- 22
units. The high and low pressure switches can be identified
by their pink stripe on the switch’s electrical wires.
The R- 410A two- stage heat pump contains a loss of
charge switch in the suction line on the *CH6 and *CH9, and
in the liquid line on *CH6 models which opens at 23 PSI and
closes at 55 PSI. See troubleshooting section for sequence
when a pressure switch trip occurs.
Muffler, Accumulator, Reversing Valve (RVS)
The R- 410A two- stage air conditioners and heat pumps
have a compressor discharge line muffler, to dampen sound
pressure pulsations.
The R- 410A two- stage heat pumps have a specifically
designed reversing valve, for R- 410A application and an
accumulator for storing excess liquid refrigerant during the
heating mode to prevent damaging flood- back.
Thermis tors
Outdoor Ambient Thermistor
The R- 410A two- speed air conditioner and heat pump units
have an outdoor ambient air thermistor. The control board
must know the outdoor air temperature so it can activate
various functions (See Fig. 43). These functions include:
S Activating the compressor crankcase heater when
ever the outdoor unit is in the off cycle.
S The fan motor speed changes for both air
conditioner and heat pump on the ECM equipped
units.
Outdoor Coil Thermistor
(OCT)
The coil or defrost thermistor (See Figure 44) is the same
thermistor used to monitor outdoor air temperature, but used
in a different configuration. The control board must know the
coil temperature so it can activate various functions. These
functions include:
S Frost sensing on heat pumps
S Coil- vs- Ambient temperature relationship
S Low ambient cooling operation
Thermistor
Curve
The resistance vs. temperature chart enables the service
technicians to check thermistor resistance, regardless of the
temperature.
Forexample,ata60_F (15.6_C) temperature, thermistor
resistance should be around 16,000 Ohms. (See Fig. 40.)
We will talk about the thermistor in more detail when we
review the control board fault codes.
0
10
20
30
40
50
60
70
80
90
0
(-17.77)
20
(-6.67)
40
(4.44)
60
(15.56)
80
(26.67)
100
(37.78)
120
(48.89)
TEMPERATURE °F (°C)
RESISTANCE (KOHMS)
THERMISTOR CURVE
A08054
Fig. 40 – Resistance Values Versus Temperature