Carrier 38VMA Series, Service Manual, Page: 22 / 112

2. Basic Control
a. Normal Operation
Table 4 - Cooling Operation
Component Operation Remarks
Compressor Cooling Compressor control
Used for high pressure protection control, discharge pipe
temperature protection control, and compressor operating
frequency upper limit control with inverter protection control.
Outdoor unit fan (FAN A) Cooling fan control
Outdoor unit fan (FAN B) Cooling fan control
Four way valve (ST1) OFF
Electronic expansion valve (EXV A) 350P
Electronic expansion valve (EXV B) 350P
Electronic expansion valve (EXV C) PI control
Solenoid valve (SV4) 17 minutes OFF
，
3 minutes ON
Solenoid valve (SV7) Pc
≥ 536.6 psi ON
，
Pc < 478.6 psi OFF
Table 5 - Heating Operation
Component Operation Remarks
Compressor Heating Compressor control
Used for high pressure protection control, low pressure
protection control, discharge pipe temperature protection
control, and compressor operating frequency upper limit
control with inverter protection control.
Outdoor unit fan (FAN A) Heating fan control
Outdoor unit fan (FAN B) Heating fan control
Four way valve (ST1) ON
Electronic expansion valve (EXV A) Heating EXV control
Electronic expansion valve (EXV B) Heating EXV control
Electronic expansion valve (EXV C) 0P
Solenoid valve (SV4) 17 min OFF
，
3min ON
Solenoid valve (SV7) Pc
≥ 507.6 psi ON
，
Pc < 420.6 psi OFF
NOTE: Heating operation is not functional at an outdoor air temperature of 77°F or more.
b. Capacity Calculation
Table 6 - Cooling Calculation
Indoor Unit
Capacity (BTU)
Indoor Unit
Capacity x 100W
Indoor Unit
Capacity (HP) A
Indoor Unit Capacity
(BTU)
Indoor Unit Capacity
x 100W
Indoor Unit Capacity
(HP) A
6000 15, 17 0.5 36000 112 4.0
7000 22, 25 0.8 42000 125 4.5
9000 28 1.0 48000 140 5.0
12000 32, 36 1.2 54000 160 6.0
13000 40 1.4 60000 180 6.5
15000 45, 50 1.7 66000 200 7.0
18000 56 2.0 72000 224, 252 8.0
21000 63 2.2 96000 280 10.0
24000 71 2.5 120000 335 12.0
27000 80 3.0 144000 400 14.0
30000 90 3.2 168000 450 16.0
33000 100 3.6 192000 560, 580 20.0
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