Fisher PTTW-10-EC Series Engineering Manual page 26

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THROUGH THE WALL UNIT
2.2.6.1.3 On-board electric heater protection
a. On-board electric heater, when the indoor fan or compressor stops working, the electrical
heater cannot be turned on.
b. When there is a problem with the room temperature sensor, auto electrical heater will not
work.
2.2.6.1.4 On-board electric heater overheat protection
When indoor coil temperature ≥55°C, electrical heater turns off. It turns on again until indoor
coil temperature ≤ 48°C.
2.2.6.2 PTC ELECTRIC HEATER SPEAKER
2.2.6.2.1 Manual PTC electrical heater function (manual ON/OFF)
When the unit is under heating mode, press the electric heater power button from on-board
control panel or IR-handset to activate the electric heater functionality (electric heater LED
indicator will light up). Press the same button again to disable the electric heater function.
PTC electric heater will turn-on when the following conditions are fulfilled:
a. Room temperature RT≤26 °C
b. When RT ≤ Ts+ 1 °C, PTC would be on after 1 second delay.
When RT＞Ts + 3 °C, PTC would be off.
c. Indoor coil temperature < 55°C
Note: if any of the above condition is not fulfill, PTC electric heater will turns off. It will turns on
again until a,b,c conditions fulfilled unless the PTC electric heater function is disabled..
2.2.6.2.2 PTC electrical heater speakers overheat protection:
When indoor coil temperature ≥55°C, electrical heater turns off. It turns on again until indoor
coil temperature ≤ 48°C.
IMPORTANT NOTE: Select either On-board electric heater or PTC electric heater speakers.
On-board electric heater and PTC electric heater speakers cannot be presented at the same
time.