When the
48 Series
When
When evaporator fan starts, air¯ow switch closes, closing induced draft contactor, and induced draft motor starts.
Centrifugal switch closes. Pilot valve opens, allowing gas to ¯ow to
The spark ignitor will continue to spark for 90 seconds until pilot ¯ame is sensed. If the pilot fails to ignite or the sensor fails to detect ¯ame, the pilot valve closes and the spark ignitor shuts off for 300 seconds (5 minutes). During this time the induced draft motor remains on to purge any unburnt gas from the combustion tubes. This ignition se- quence will repeat inde®nitely.
When additional heat is needed, W2 is energized. Pilot valve no. 2 opens, allowing gas to ¯ow to
When the
50 Series Units Ð Unit power on, system selector switch set at HEAT position, fan switch set at AUTO. position.
On a call for heating, W1 on the thermostat closes, and evaporator fan and the ®rst stage of electric heat are ener- gized. On a further drop in room temperature, W2 on the thermostat closes, energizing the second stage of electric heat.
NOTE: Units equipped with low electric heat option have only one stage. Reset thermostat to a setting below room temperature. Electric heat and evaporator fan shut off.
COOLING, UNITS WITH ECONOMIZER Ð With sub- base switch set at COOL position and fan switch set at AUTO. position, evaporator fan is energized when Y1 on thermostat closes. If enthalpy is below setting on enthalpy switch, the economizer
NOTE: If fan switch is ON position and the room thermostat is satis®ed, the
HEATING, UNITS WITH ECONOMIZER Ð Operation is the same as described in Heating, Units Without Econo- mizer sections on page 41, except that the
AUTOMATIC CHANGEOVER USING AUTOMATIC CHANGEOVER THERMOSTAT Ð Turn unit power on. Set system selector switch at AUTO. position.
When the temperature of the conditioned space rises to the cooling selector lever setting, unit automatically switches from heating to cooling mode. When the temperature of the conditioned space falls to the heating selector switch setting, unit automatically changes from cooling to heating mode. The thermostat is interlocked so that cooling and heating sys- tems do not operate at the same time.
Head Pressure Control Ð All units have a fan cy- cling thermostat which cycles the no. 2 condenser fan. This switch opens at 60 F ± 3° F and closes at 70 F ± 3° F. This allows the unit to operate down to 45 F outdoor ambient temperature.
NOTE: Accessory −20 F Low Ambient Kit is available, which allows mechanical cooling to −20 F outdoor ambient. See accessory installation instructions for mounting and opera- tion details.
SERVICE
Service Access Ð All unit components can be reached through clearly labeled hinged access doors. These doors are not equipped with tiebacks, so if heavy duty servicing is needed, either remove them or prop them open to prevent accidental closure.
Each door is held closed with 3 latches. The latches are secured to the unit with a single
To open, loosen the latch bolt using a
NOTE: Disassembly of the top cover may be required under special service circumstances. It is very important that the orientation and position of the top cover be marked on the unit prior to disassembly. This will allow proper replace- ment of the top cover onto the unit and prevent rainwater from leaking into the unit.
IMPORTANT: After servicing is completed, make sure door is closed and relatched properly, and that the latches are tight. Failure to do this can result in water leakage into the
COMPRESSORS
Sizes 034 and 044 Ð Access to the compressors is through the doors on the condenser end of the unit. This door also provides access to the discharge and suction service valves, the crankcase heaters, and the high- and
Sizes
42
