Service and Parts Manual (2018, 2019, 2020, 2021, 2022)

21 PB
OPERATION
Function and Control
2) Heating Mode
Working condition and process for heating:
When T1≤Ts -2°F(1°C), the unit is running in heating mode. Heat pump or electric heating will start depending
on the ambient temperature condition or the heating priority setting (#4 DIP SWITCH, ON- for heat pump and
OFF-for electric heating).
When T1≥Ts+ 2°F(1°C), the heating is turned OFF. Meanwhile, the fan will run at the setting fan speed for 15s
or 1 minute delay (CONSTANT FAN OFF) or run at the setting speed continuously (CONSTANT FAN ON).
When Ts-2°F(1°C) <T1<Ts+ 2°F(1°C), the unit keeps at the previous running status.
Electric heater does not work with heat pump at the same time. When T1<41°F (5°C) unit will run the
Electric heater, when T1≥41°F (5°C) the unit will run heat pump.
3) Room Freeze Protection (AUTO HEATING)
This is valid only in standby mode. The dual 8 digital tube displays “L0”.
Entry condition: If #5 DIP SWITCH is set to ON to enable the indoor freeze protection and the main board
detects the indoor ambient temperature lower than 50°F (10°C) for 3 minutes successively .
Quitting condition: When indoor ambient temperature rises to 55 °F(13°C), heating will stop.
4) Temperature Sensor Open Circuit or Short Circuit Protection
If the temperature sensor is an open circuit or a short circuit, the ERROR CODE will display on the digital
tube. If the malfunction of temperature sensor is detected for 30s, the unit will turn off.
1) 8 DIP Switch Function
(after reprogramming, disconnect the power cord and then power up again to make it effec tive)
Warning: #2 and #3 should be matched the unit type,but #2 can be switched to OFF to set as Emergency Heat
Override! This will cause the E-heater to run all the time.
1 Reserved
2 Heat pump
ON- valid; OFF-invalid
3 E-heater
ON- valid; OFF-invalid
4 Heating priority
ON-heat pump to be prior; OFF-Electric heat to be prior
5 Room freeze protection
ON- valid; OFF- invalid
6 Auto-restart
ON- valid; OFF- invalid
7 Medium fan speed for indoor fan
ON-when HIGH fan speed,is selected the output will be medium speed instead; OFF-
output is the same speed as selected.
8 Reserved