Four-Way Valve Control; Electronic Expansion Valve (Exv) Control - Lennox MMA018SM4 Service Manual

19.8.2. Heating Mode
Normally the system will choose the running fan speed according to ambient temperature:

19.9. Four-Way Valve Control

In heating mode, four-way valve is opened. In defrosting, four-way valve operates according to defrosting action.
In other modes, four-way valve is closed. When the heating mode to other modes, the four-way valve is off after
compressor is off for 2 minutes. Failure or protection (not including discharge temperature protection, high and low
pressure protection), four-way valve immediately shuts down.

19.10. Electronic Expansion Valve (EXV) Control

a. EXV will be fully closed when turning on the power. Then EXV will be standby with 350P open and will open to target
angle after compressor starts.
b. EXV will close with -160P when compressor stops. Then EXV will be standby with 350P open and will open to target
angle after compressor starts.
c. The action priority of the EXVs is A-B-C-D.
d. Compressor and outdoor fan start operation only after EXV is initialized.
19.10.1. Cooling mode
The initial open angle of EXV is 250P, adjustment range is 100-350p. When the unit operates for three minutes,
the outdoor will receive indoor units( of capacity demand) T2B information and calculate the average of them.
After comparing each indoor's T2B with the average, the outdoor gives the following modification commands: If the
T2B>average, the relevant valve opens 16p (pulses) more. If the T2B= average, the relevant valve's open range
remains; If the T2B<average, the relevant valve closes 16p (pulses) more.
This modification will be carried out every 2 minutes.
19.10.2. Heating mode
The initial open angle of EXV is 250P, adjustment range is 100-350p. When the unit start to work for 3 minutes, the
outdoor will receive indoor units (of capacity demand) T2 information and calculate from subject received, size and
categories.
After comparing each indoor's T2 with the average, the outdoor gives the following modification commands: If the
T2>average+2, the relevant valve needs closes 16p (pulses) more.
If average+2≥the T2≥ average-2, the relevant valve's open range remains.
If the T2<average-2, the relevant valve opens 16p (pulses) more.
This modification will be carry out every 2 minutes.
T4
E DC_FAN_SSLOW_SPD_ADD
21℃
19℃
D DC_FAN_SLOW_SPD_ADD
18℃
16℃
C DC_FAN_MIN_SPD_ADD
15℃
13℃
B DC_FAN_MID_SPD_ADD
12℃
10℃
A DC_FAN_HI_SPD_ADD
83