Fisher PTTW-10-EC Series Engineering Manual page 24

2.2.4.2 Conditions of compressor working：
a. Compressor starts: RT≤ST+1℃；
b. Compressor stops: RT＞ST+3℃；
c. +1℃＜ST-RT≤+3℃，compressor maintains the original state.
2.2.4.3 The first time the unit is turned on, there will be a 3 minute delay for compressor
protection before temperature starts to rise.
2.2.4.4 Operation of four-way valve：In heating mode, the four-way valve remains open
(except when defrosting). When heating mode is selected or unit is turned on, the four-way
valve will open 5 minutes before compressor starts. When mode is changed from heating
mode or unit is turned off, four-way valve will close after compressor has stopped for 2
minutes.
2.2.4.5 Operation of outdoor motor: Starts and stops at the same time as the compressor
(Except when system goes into the defrost function or over heat protection).
2.2.4.6 Indoor auto fan speed selection.
2.2.4.7 Pre-heat control: After selecting heating mode, when IPT≥38℃, indoor fan motor will
run according to the setting. When IPT＜38℃, indoor fan motor will delay starting until
compressor runs for 60 seconds.
In heating mode, when the unit has been heating for 30 minutes or more and the compressor
is continuously running for 5 minutes, the outdoor coil temperature sensor starts detecting the
outdoor coil temperature. When the sensor detects <-5 degree for 1 minute, and above 2
conditions are met, the unit will begin to defrost.
When defrosting, if the compressor has run for 5 minutes and OPT rises to 15℃, defrosting
will stop automatically and normal heating will resume.
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