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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 user
interface. To bypass this feature, momentarily short and
release Forced Defrost pins.
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 Evolution 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 On 226A, 266A, 286A models there is a 1 minute time
delay between staging from low to high and from high to
low capacity. On 288A 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 Puronr 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 Puronr two--stage heat pump contains a loss of charge switch
in the suction line on 286BNA and 288ANA, and liquid line on
226A and 266A 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 Puronr two--stage air conditioners and heat pumps have a
compressor discharge line muffler, to dampen sound pressure
pulsations.
The Puronr two--stage heat pumps have a specifically designed
reversing valve, for Puronr application and an accumulator for
storing excess liquid refrigerant during the heating mode to prevent
damaging flood--back.
Thermistors
Outdoor Ambient Thermistor
The Puronr 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.
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 is the same thermistor used to
monitor outdoor air temperature. 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.
For example, at a 60_F temperature, thermistor resistance should
be around 16,000 Ohms. (See Fig. 34.)
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. 34 – Resistance Values Versus Temperature