Form O-Y, PN 273647R5, Page 26
3.7 Compressor
Operation,
Maintenance,
and
Replacement
(cont'd)
Record the ambient temperature. Adjust the system controller so that a call for
cooling exists.
NOTE:
Outdoor ambient lockouts may prevent mechanical cooling. Temporarily
override lockouts by lowering the cooling setpoint. When testing is complete, reset
the controller.
Because it is possible to unknowingly connect 3-phase power in such a way
as to cause the scroll compressor or blower to rotate in reverse, it is very
important to check this on startup.
Check Compressors - Immediately at startup, observe the gauges.
If the
suction pressure rises and discharge pressure drops, the compressor is
operating in reverse and must be shut down. Turn off the power and switch
the 3-phase line voltage wiring connections before restarting the unit.
Important:
If allowed to operate for several minutes in reverse, the compressor’s
internal protector will trip. If a compressor is repeatedly allowed to restart and run
in reverse, the compressor will be permanently damaged.
•
Step 11
.
Check Subcooling and Superheat
Superheat is
the verification that the evaporator coil is properly using the
refrigerant supplied. Too much superheat indicates that the coil is undercharged.
Too little superheat indicates that the coil is overcharged and potentially flooding
liquid refrigerant to the compressor.
Subcooling is
the measurement of liquid refrigerant stored in the condenser coil.
Too much subcooling indicates a system overcharge. Too little subcooling indicates
a system undercharge and may not provide the thermal expansion valve with a full
column of liquid refrigerant for proper operation.
Two important requirements before checking superheat and subcooling:
1) This unit has fully intertwined refrigerant circuits and each circuit MUST be
isolated before measuring its temperature. Another active circuit will influence the
reading and make it impossible to determine accurate superheat and subcooling.
2) If equipped with an optional hot gas bypass, disable the hot gas bypass valve
before charging. Locate the shutoff valve between the compressor discharge and
the hot gas bypass valve. Disable the hot gas bypass valve by closing the shutoff
valve. When measurements are complete, be sure to open the valve.
IMPORTANT:
Do not release refrigerant to the atmosphere!
If required
service procedures include the adding or removing of refrigerant, the
qualified HVAC service technician must comply with all federal, state
or
provincial, and local laws.
Follow the procedures in Paragraph 3.6 on page 17 to check subcooling and
superheat.
•
Step 12
. (Select the procedure that applies.)
IF the oil measured in Step 2
was significantly less than in the table on
page 22 or the acid test in Step 2 indicated a burnout, do the following:
a)
Operate the unit for several hours. Check the pressure drop through the
temporary suction line filter drier. If the pressure drop exceeds 8 psig, recover
the refrigerant, replace the suction line filter drier with the same type as
removed, replace the liquid line filter drier, evacuate the circuit, and re-charge
with the recovered refrigerant.
Continue to monitor the pressure drop through the suction line filter drier and
repeat the process above until the pressure does not exceed 8 psig after several
hours of operation. (
NOTE
: System must be allowed to run no more than 72
hours with a suction line filter drier.)
b) Allow the system to operate for 4-8 hours. Recover the refrigerant and take an
oil sample. Retest the oil for acid.
c) If the test for acid is negative
, remove the suction line filter drier, replace
the liquid line drier, evacuate, and re-charge the system with the recovered
refrigerant.
If the test indicates acid
, replace both the liquid line filter drier and the suction
line filter drier and repeat b) and c).
3.0 Maintenance/Service Procedures - Unit & Cooling (cont'd)
