HTR Ð Heater
*AFS1 deenergizes control circuit if loss of outdoor air occurs.
Fig. 35 Ð Major Component Identi®cation (Typical
When OAT is open, ®nal stage heating element in all zone modules is inactive. When OAT is closed, ®nal stage heating element in a zone module may be energized whenever second- stage thermostat for that zone module calls for heat as follows:
UNITS WITH 2-ELEMENT HEATERS
OAT Open Ð One element energized
OAT Closed Ð Two elements energized
UNITS WITH
OAT Open Ð Two elements energized
OAT Closed Ð Three elements energized
Optional Glycol Heating Coils Ð Start up glycol solution supply system in accordance with equipment manu- facturer's instructions. Solution supply temperature must not exceed 200 F. Maximum solution ¯ow through each zone module heating coil is 6 gpm.
Zone Air¯ow Adjustment Ð Adjust each zone duct balancing damper to provide required air¯ow to each zone. Increasing or decreasing air¯ow to one zone may cause a change in the air¯ow to other zones. After initial damper settings have been made, repeat the adjustment procedure, as required, to be sure ®nal desired air¯ows are achieved. Do not go below 600 cfm or above 1200 cfm per zone module.
Be sure that temperature rise is within range shown on unit instruction plate and Table 1 (48MA only).
Sequence of Operation Ð When unit power is on and no zone thermostat is calling for cooling or heating, the evaporator fan and crankcase heater(s) are on. The outdoor- air dampers are at the
COOLING Ð On a call for cooling from a zone thermostat, compressor no. 1, with unloader(s), starts; the liquid line so- lenoid for that zone evaporator coil opens; and condenser- fan motor no. 1 starts. Compressor will load or unload in response to suction pressure as required. As additional cool- ing is required (i.e., more zones call for cooling), compres- sor no. 2 (no unloaders) will be energized
If heat load is not sufficient to maintain operation of com- pressor no. 1 in an unloaded condition, hot gas bypass valve will meter hot gas to outdoor air evaporator coil to supply additional load. On 48MA and 50ME040, hot gas is intro- duced into evaporator whenever required to eliminate un- loader
The Motormaster head pressure control device will vary speed of
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