Carrier 50ZH024-060 - Manual (Page 15)

UNIT CONTROLS — All compressors have the following
internal-protection controls.
High-Pressure Relief Valve — This valve opens when the
pressure differential between the low and high side becomes
excessive (size 024 unit has temperature relief only).
Compressor Overload — This overload interrupts power to
the compressor when either the current or internal tempera-
ture become excessive, and automatically resets when the
internal temperature drops to a safe level.
This overload may require up to 60 minutes (or longer) to
reset; therefore, if the internal overload is suspected of being
open, disconnect the electrical power to the unit and check
the circuit through the overload with an ohmmeter or con-
tinuity tester.
SEQUENCE OF OPERATION — When power is supplied
to unit, the transformer (TRAN) is energized.
Cooling — With the thermostat subbase in the cooling po-
sition, and when the space temperature comes within 2° F of
the cooling set point, the thermostat makes circuit R-O. This
energizes the reversing valve solenoid (RVS) and places the
unit in standby condition for cooling.
As the space temperature continues to rise, the second stage
of the thermostat makes, closing circuit R-Y. When com-
pressor time delay (5 ± 2 minutes) is completed, a circuit is
made to contactor (C), starting the compressor (COMP) and
outdoor-fan motor (OFM). Circuit R-G is made at the same
time, energizing the indoor-fan relay (IFR) and starting the
indoor-fan motor (IFM) after 1-second delay.
When the thermostat is satisfied, contacts open, deener-
gizing C. The COMP and OFM stop, and the IFM stops
after a short time delay. The reversing valve solenoid is
deenergized.
Heating — On a call for heat, thermostat makes circuits R-Y
and R-G. When compressor time delay (5 ± 2 minutes) is
completed, a circuit is made to C, starting COMP and OFM.
Circuit R-G also energizes IFR and starts IFM after 1-second
delay.
Should room temperature continue to fall, circuit R-W is
made through second-stage thermostat bulb. If optional elec-
tric heat package is used, a relay is energized, bringing on
first bank of supplemental electric heat. When thermostat is
satisfied, contacts open, deenergizing contactor and relay; mo-
tors and heaters deenergize. The IFM may be controlled by
a time-delay relay that keeps the fan on for 30 seconds.
Defrost — Defrost board (DB) is a time and temperature
control, which includes a field-selectable time period be-
tween checks for defrost (30, 50, and 90 minutes). The time
period is factory-set at 30-minutes and should only be ad-
justed by a trained service person. Electronic timer and de-
frost cycle start only when contactor is energized and defrost
thermostat (DFT) is closed.
Defrost mode is identical to Cooling mode, except outdoor-
fan motor stops and a bank of optional electric heat turns on
to warm air supplying the conditioned space.
MAINTENANCE
To ensure continuing high performance, and to reduce the
possibility of premature equipment failure, periodic main-
tenance must be performed on this equipment. This heating
and cooling unit should be inspected at least once each year
by a qualified service person. To troubleshoot cooling of units,
refer to Troubleshooting chart in back of book.
NOTE TO EQUIPMENT OWNER: Consult your local dealer
about the availability of a maintenance contract.
The ability to properly perform maintenance on this
equipment requires certain expertise, mechanical skills,
tools and equipment. If you do not possess these, do not
attempt to perform any maintenance on this equipment,
other than those procedures recommended in the User’s
Manual. FAILURE TO HEED THIS WARNING COULD
RESULT IN SERIOUS PERSONAL INJURY AND
POSSIBLE DAMAGE TO THIS EQUIPMENT.
The minimum maintenance requirements for this equip-
ment are as follows:
1. Inspect air filter(s) each month. Clean or replace when
necessary.
2. Inspect indoor coil, outdoor coil, drain pan, and conden-
sate drain each cooling season for cleanliness. Clean
when necessary.
3. Inspect blower motor and wheel for cleanliness each cool-
ing season. Clean when necessary. For first heating sea-
son, inspect blower wheel bimonthly to determine proper
cleaning frequency.
4. Check electrical connections for tightness and controls
for proper operation each cooling season. Service when
necessary.
5. Check the drain channel in the top cover periodically for
blockage (leaves, insects). Clean as needed.
Failure to follow these warnings could result in serious
personal injury:
1. Turn off electrical power to the unit before perform-
ing any maintenance or service on the unit.
2. Use extreme caution when removing panels and parts.
As with any mechanical equipment, personal injury
can result from sharp edges.
3. Never place anything combustible either on, or in con-
tact with, the unit.
Air Filter
Never operate the unit without a suitable air filter in the
return-air duct system. Always replace the filter with the
same dimensional size and type as originally installed.
See Table 1 for recommended filter sizes.
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