Carrier 38AH024-034 - Manual (Page 15)

Next, close the compressor circuit breakers and then re­
set space thermostat TCI below ambient so that a call for
stage one cooling is ensured. If compressor does not start,
set thermostat lower.
NOTE: Do not use circuit breakers to start and stop the
compressor except in an emergency.
If 38AH is connected to a single 2-stage cooling thermo­
stat (one fan coil), start-up of circuit no. 1 compressor will
be delayed from one second to 5 minutes from the time the
call for cooling is initiated (see Fig. 12). TC2 (thermostat
contacts 2) close l'/
2 ° F (0.7° C) lower than TCI. After
these contacts close, start up of circuit no. 2 compressor
will be delayed from one second to 5 minutes from the time
the call for cooling is initiated (see Fig. 12).
A CAUTION
Never charge liquid into the low-pressure side of sys­
tem. Do not overcharge. During charging or removal
of refrigerant, be sure indoor-fan system is operating.
Adjust Refrigerant Charge
NOTE: Actual start-up and all refrigerant charge modifica­
tions should be done only under supervision of a qualified
refrigeration mechanic.
With all fans operating, adjust the refrigerant charge in ac­
cordance with the unit charging charts located on the inside
of the control box doors and in Fig. 11.
Measure pressure at the liquid line service valve, being
sure Schrader depressor is used if required. Also, measure
liquid line temperature as close to the liquid service valve
as possible. Add charge until the pressure and temperature
conditions of the charging chart curve are met. If liquid
pressure and temperature point fall above curve, add charge.
If liquid pressure and temperature point fall below curve,
reduce the charge until the conditions match the curve.
If the sight glass is cloudy, check refrigerant charge again.
Ensure all fans are operating. Also ensure maximum
allowable liquid lift has not been exceeded. If charged per
chart and if the sight glass is still cloudy, check for a plugged
filter drier or a partially closed solenoid valve. Replace or
repair, as needed.
Check Compressor Oil Level — After adjusting the
refrigerant charge, allow each circuit to run fully loaded for
20 minutes. Running oil level should be within view of the
crankcase sight glass. Stop the compressors at the field power
supply disconnect and check the crankcase oil level. Add
oil only if necessary to bring the oil into view in the sight
glass. If oil is added, run the circuit for an additional 10
minutes, then stop and check oil level. If the level remains
low, check the piping system for proper design for oil re­
turn; also, check the system for leaks.
If the initial check shows too much oil (too high in the
sight glass) remove oil to proper level. See Preliminary Oil
Charge, page 14, for proper procedure for adding and re­
moving oil.
When the above checks are complete, repeat the proce­
dure with the unit operating at minimum load conditions.
For this minimum load check, operate each circuit’s com­
pressor individually and unloaded to minimum step.
Unload the compressor(s) by turning the control set point
adjustment nut counterclockwise until the adjustment nut
stops. The unloader is now at 0 psig (0 kPag) set point. If
electric actuated unloaders are installed, energize the sole­
noid to unload the compressor.
Return unloader to original setting after checks are
complete.
Final Checks — Ensure all safety controls are operat­
ing, control panel covers are on, and the service panels are
in place.
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