Four-Way Valve Control - Carrier 38MGR Series Service Manual

Heating Mode
The initial open angle of EXV is 250P, dependent on indoor model
size, adjustment range is 100-400p. After the unit works for three
minutes, the outdoor unit receives the indoor units (of capacity
demand) T2 information and calculates the their average. After
comparing each indoor units' T2 with the average, the outdoor unit
gives the following modification commands.
If the T2<average +2, the relevant valve needs more 16p close. If
average +2 the T2 average.2, the relevant valve's open range
≥ ≥
remains. If the T2< average.2, the relevant valve needs more 16p
open. This modification occurs every two minutes.
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Four-way valve control

In Heating mode, the four-way valve opens. In Defrosting mode, the
four.way valve operates in accordance to the Defrosting action. In
other modes, the four-way valve is closed.
When the Heating mode changes to other modes, the four-way valve
closes after the compressor is off for two minutes. Failure or
protection (not including discharge temperature protection, high and
low pressure protection), the four-way valve immediately shuts down.
Specifications subject to change without notice. 38MGR-04SM