25HPA6
2.If the expected result is not achieved, remove the solenoid plug from the compressor and with the unit running and the User Interface or thermostat calling for high stage, test the voltage output at the plug with a DC voltmeter. The read- ing should be 24 volts DC.
3.If the correct DC voltage is at the control circuit molded plug, measure the compressor unloader coil resistance. The resistance should be 32 to 60 ohms depending on com- pressor temperature. If the coil resistance is infinity, much lower than 32 ohms, or is grounded, the compressor must be replaced.
Temperature Thermistors
Thermistors are electronic devices which sense temperature. As the temperature increases, the resistance decreases. Thermistors are used to sense outdoor air (OAT) and coil temperature (OCT). Refer to Fig. 7 for resistance values versus temperature.
THERMISTOR CURVE
| 90 | |
(KOHMS) | 80 | |
70 | ||
| ||
| 60 | |
RESISTANCE | 50 | |
20 | ||
| 40 | |
| 30 | |
| 10 | |
| 0 |
0 | 20 | 40 | 60 | 80 | 100 | 120 |
(4.44) | (15.56) | (26.67) | (37.78) | (48.89) | ||
|
| TEMPERATURE °F (°C) |
|
| ||
A08054
Fig. 7 - Resistance Values Versus Temperature
If the outdoor air or coil thermistor should fail, the control will flash the appropriate fault code. (See Table 4.)
OAT Thermistor must be locked in place with spherical nib end facing towards the front of the control box
Fig. 8 - Outdoor Air Thermistor (OAT) Attachment
IMPORTANT: The outdoor air thermistor and coil thermistor should be factory mounted in the final locations. Check to ensure thermistors are mounted properly per Fig. 8 and Fig. 9.
Thermistor Sensor Comparison
The control continuously monitors and compares the outdoor air temperature sensor and outdoor coil temperature sensor to ensure proper operating conditions. The comparison is:
SIn cooling if the outdoor air sensor indicates ≥ 10_F
(≥ 5.6_C) warmer than the coil sensor (or) the outdoor air sensor indicates ≥ 20_F (≥ 11_C) cooler than the coil sensor, the
sensors are out of range.
SIn heating if the outdoor air sensor indicates ≥ 35_F (≥ 19.4_C) warmer than the coil sensor (or) the outdoor air sensor indicates ≥ 10_F (≥ 5.6_C) cooler than the coil sensor, the sensors are out of range.
If the sensors are out of range, the control will flash the appropriate fault code as shown in Table 4.
The thermistor comparison is not performed during low ambient cooling or defrost operation.
Failed Thermistor Default Operation
Factory defaults have been provided in the event of failure of outdoor air thermistor (OAT) and/or outdoor coil thermistor (OCT).
If the OAT sensor should fail, low ambient cooling will not be allowed and the
If the OCT sensor should fail, low ambient cooling will not be allowed. Defrost will occur at each time interval during heating operation, but will terminate after 5 minutes.
If there is a thermistor out of range error, defrost will occur at each time interval during heating operation, but will terminate after 5 minutes.
Count the number of short and long flashes to determine the appropriate flash code. Table 4 gives possible causes and actions related to each error.
OCT Thermistor must be secured tight on stub tube.
Fig. 9 - Outdoor Coil Thermistor (OCT) Attachment
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