Refrigeration Maintenance
132
3. Open both service manifold hand valves.
4. Set all zones to run in Low Speed Cool
through the HMI Service Test Mode. Refer to
the SPECTRUM TS Microprocessor
Diagnostic Manual (TK 51652) for
information about the Service Test Mode.
5. Front seat the receiver tank outlet valve.
6. Run the unit until a 3 to 5 psig [21 to 35 kPa]
reading is obtained on the suction gauge, then
stop the unit.
7. Back seat the suction service valve and the
receiver tank outlet valve.
8. Remove all remaining hoses.
9. Install and tighten the service port and valve
stem caps.
10. Unit is ready for a functional check out.
Refrigerant Leaks
Use a reliable leak detector (e.g., electronic
detector) to leak test the refrigeration system.
Inspect for signs of oil leakage which is the first
sign of a leak in the refrigeration system.
NOTE: It is normal for compressor shaft seals to
have a slightly oily film.
Refrigerant Charge
Testing the Refrigerant Charge with
an Empty Box
If the unit has an insufficient charge of refrigerant,
the evaporator will be “starved” and the box
temperature will rise even though the unit is
operating. The suction pressure will drop as the
refrigerant charge decreases. The charge may be
determined by inspection of the refrigerant
through the receiver tank sight glass with the
following conditions established:
1. Place a test box over the evaporator in each
zone to separate the zones.
2. Install a gauge manifold.
3. Set all zones to run in High Speed Cool
through the HMI Service Test Mode. Refer to
the SPECTRUM TS Microprocessor
Diagnostic Manual (TK 51652) for
information about the Service Test Mode.
4. Run the unit with all zones in high speed cool
until the air in the box in each zone indicates
0 F (-18 C). By allowing a box to leak a small
amount, you will be able to maintain 0 F
(-18 C).
5. The discharge or head pressure gauge should
read 290 to 310 psig (1999 to 2137 kPa).
If the pressure is below this, it can be raised by
covering a portion of the condenser coil with a
piece of cardboard.
6. The compound gauge should be indicating 12
to 20 psig (83 to 138 kPa) gauge pressure.
If there is any doubt about the unit gauge,
check the calibration.
7. Under these conditions, the ball in the receiver
tank sight glass should be floating. If there is
no indication of refrigerant in the receiver tank
sight glass, the unit is low on refrigerant.
Testing the Refrigerant Charge with
a Loaded Box
1. Install a gauge manifold (optional).
2. Run the unit with all zones on the Cool cycle.
3. Cover at least three quarters of the condenser
to drive any excess refrigerant from the
condenser into the receiver tank.
4. As the head pressure is rising, check the
receiver tank sight glass. The ball should be
floating. If there is no indication of refrigerant
in the receiver tank sight glass, the unit is low
on refrigerant.
NOTE: If the ball floats, there is sufficient
refrigerant in the unit for that load at that
particular box temperature. This test does
not determine if the unit contains a full
charge of refrigerant.
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