HEATING (48MA) Ð On call for heating from a zone, the forced draft blower will start and the pilot will light. The zone burner will ignite after the pilot has been proven. (Ap- proximately 60 seconds.)
NOTE: A
HEATING (50ME WITH ELECTRIC HEAT) Ð On a call for heating from a zone, the
Heating Lockout (50ME with Electric Heat) Ð If any zone module is operating on mechanical cooling (Compressor[s] is operating), one heating element in each zone module is locked out and zone module cannot be energized. Operation of lockout circuit is independent of
HEATING (50ME WITH GLYCOL HEATING COILS) Ð On a call for heating from a zone, the heating relay and heat- ing coil solenoid valve for that zone are energized. If 2 or more unit zone modules are joined to serve a common zone, stage 2 of heating thermostat operates remaining heating relays and solenoid valves depending on connection arrangement.
SERVICE
Cabinet Panels and Grilles
SIDE PANELS Ð To remove a panel, remove lower screw on
TOP PANELS Ð Remove end caps from each end of rain covers. Remove panel screws and lift off panels as required. Save end caps and screws for reinstallation.
HEATER ACCESS PANELS Ð See Side Panels section above.
Cleaning Ð Inspect unit interior at the beginning of each heating and cooling season and during each season as op- erating conditions require. Remove unit side panels and top panels to expose unit interior as required.
EVAPORATOR COILS (ZONE COOLING COILS) AND GLYCOL HEATING COILS Ð Clean with a stiff brush, vacuum cleaner, or compressed air.
CONDENSER AND
ÐClean with a stiff brush or vacuum cleaner. If cleaning with compressed air or
CONDENSATE DRAINS Ð Check and clean annually at start of cooling season.
GAS HEATING SECTION Ð Inspect burners and heat ex- changers before each heating season. Remove exhaust grilles to inspect heat exchangers. Clean with wire brush if there is any accumulation of debris. The main burners should also be cleaned if there is any accumulation of debris. Fire each zone to be assured of proper operation. Correct pilot height is 1 to 11¤2 inches.
COMBUSTION AIR FAN Ð Inspect blower wheel for dirt, and remove and clean if necessary.
Air¯ow Switches
INDOOR AIRFLOW SWITCH (AFS1) Ð This switch is located in evaporator fan inlet venturi. This switch will shut down unit if air¯ow through zone modules is insufficient.
COMBUSTION AIRFLOW SWITCH (AFS2) Ð This switch (48MA only) is located in combustion air plenum. This switch will shut down unit heating mode if combustion air is in- sufficient. See
Service Switch Ð A control circuit service switch is located in the power and condensing control box (Fig. 34 and 35). Shut down unit (compressors, fans, and control cir- cuits) at this switch.
Do not use compressor circuit breakers to start and stop compressors except in emergency.
Time Guard Control Circuit Ð Each compressor circuit has a
On
Capacity Control Pressure Switches (CCP)
1.CCP1 is open (opens at 63 psig; closes at 83 psig). This prevents cycling of compressor no. 2 at
2.CCP2 is closed (opens at 54 psig; closes at 78 psig).
3.Holding relay no. 2 (HR2) is deenergized.
When the suction pressure reaches 83 psig, CCP1 closes to energize HR2 and compressor no. 2. Compressor no. 2 will then be operated by CCP2.
Compressor Oil Ð Compressors have their own oil sup- ply. Compressor crankcases on
Compressor data is shown in Table 1 and on dataplate at- tached to compressor body. Refer to 06D or 06E Compres- sor Service Manual for additional compressor service information.
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