IM 817-4
Page 31 of 60
Checking System Charge
The system charge should be checked under design conditions [95ºF
outside air, 80ºF/67ºF (DB/WB) indoor air]. Refer to condensing unit
manufacturer's guidelines.
Before adjusting refrigerant charge, verify that the unit ventilator is
operating at normal design cfm. Nominal cfm is determined with a dry
coil, and cfm will be reduced during air conditioning operation with a
wet coil. Filters and coil must be clean and fan speed set at high.
temperature to obtain subcooling.
Typical conditions - 95
º
F ambient, 75 psig suction, 285 psig head
pressure, 6-7
º
F superheat, 15
º
F subcooling.
Liquid
Line
Drier
Hazardous Voltage!
Disconnect all electric power including remote disconnects
before servicing. Failure to disconnect power before servicing
can cause severe personal injury or death.
Sight Glass
TXV (Thermal Expansion Valve)
Insulate Bulb, (Reacts
To Refrigerant Tempera
-
ture and Not Ambient)
Insulate The Suction
Line Piping, (Minimum
Heat Pickup)
Return (Suction Line)
Supply (Liquid Line)
Figure 88 - Insulate Bulb and Suction Line Piping
Figure 89 - Typical Split System Evacuation/Charging Setup
Suction Line Service Valve
Liquid Line Service Valve
Outdoor Fan
Compressor
Gauge Bar Hoses
Vacuum Pump
TXV
Indoor Fans
Charging
Cylinder
Indoor Coil
Outdoor Coil
Low Pressure
Gauge
Outdoor Condensing Unit
Unit Ventilator
High Pressure
Gauge
Figure 90 - Typical Unit Ventilator/Condensing Unit Wiring Diagram
Compressor
Compressor
Contactor
Capacitor
Head
Pressure
Controller
(Optional)
Fan
Motor
High
Pressure
Switch
Low
Pressure
Switch
TDR = Time Delay Relay
TB = Terminal Block
T4
2
3
1
Rec3
Line
Vo
ltage
Factory Wired
Field Wired (By Others)
TDR or TB
Low Ambient
T
emp. Switch
To controls by others, to energize condensing unit normally
open contact.
T
1
T
2
L
2
L
1
L
2
L
1
24V
24V
Determining Subcooling
To determine correct subcooling:
1. Measure outdoor ambient. It must be between 65ºF and 105ºF.
2. Measure liquid line temperature 6 inches from the TXV inlet.
3. Measure liquid line pressure near the TXV.
4. Determine saturated liquid temperature from saturated
temperature
pressure chart (table 22).
5. Subtract measured liquid line temperature from saturated liquid
temperature to obtain subcooling.
6. Adjust charge per condensing unit manufacturer recommendation
to obtain 15 - 16ºF subcooling.
(By Others)
(By Others)
Note:
Table 21 piping dimensions are for systems with up to 30 ft. (9.14 m)
vertical separation and up to 100 ft
(30.47 m) horizontal separation from
the outdoor condensing unit.
Table 21 - Dimensions, DX Tubing inches (mm)
Models AVS, AVV,
AVB, AVR
Suction Line O.D.
Liquid Line O.D.
S07
3/4" (19mm)
1/4" (6mm)
S10
3/4" (19mm)
1/4" (6mm)
S13
7/8" (22mm)
3/8" (10mm)
S15
7/8" (22mm)
3/8" (10mm)
S20
7/8" (22mm)
3/8" (10mm)
Typical Condensing Unit
Typical Unit Ventilator Interface
Pressure
Taps
(by others)
Pressure Taps (Field Installed)
Pressure Taps
(Field Installed)
NOTICE
WARNING
