Refrigeration Maintenance
95
Refrigeration System Checks
NOTE: The Scroll compressor can not be
pumped down. Check the compressor efficiency
using the following procedure.
1. Install a gauge manifold set. Attach the
compound (low pressure) gauge to the service
port on the suction service valve. Attach the
high pressure gauge to the discharge service
port.
2. Run the unit in high speed cool until the
system pressures stabilize.
3. Note the head pressure on the high pressure
gauge.
4. Cover the condenser and check the head
pressure. The compressor should be able to
increase the head pressure at least 100 psig
(689 kPa). The compressor is probably faulty
if it cannot raise the head pressure 100 psig
(689 kPa).
Check the rest of the system by checking the
system pressures and the refrigerant flow in heat
and cool. The suction and discharge pressures
should be within the normal ranges for a standard
unit. Check the temperatures of the refrigeration
lines by hand to check the refrigerant flow.
Three-way Valve Condenser
Pressure Bypass Check Valve
The condenser pressure bypass check valve is
built into the three-way valve. This check valve
controls the bypass flow of refrigerant gas
between the condenser inlet line and compressor
discharge line.
The check valve is closed when the unit is running
on cool, or whenever the discharge pressure is
higher than the condenser pressure.
When the unit is running on defrost or heat, if the
condenser pressure is higher than the discharge
pressure, the check valve opens and the condenser
pressure is bled off until it drops to the level of the
discharge pressure. The purpose of the valve is to
improve heating/defrosting ability and three-way
valve response.
To check the operation of the valve:
1. Remove the condenser pressure bypass check
valve cap from the three-way valve.
2. Using a screwdriver, gently turn the check
valve stem in until the valve is front seated.
3. Install a service gauge manifold set on
compressor.
4. Close (front seat) the receiver tank outlet
valve.
1. Suction Service Valve
2. Compound Gauge
3. High Pressure Gauge (0 to 500 psig)
4. Discharge Service Port
Figure 50: Gauge Manifold Installation
AGA659
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