If a Y2 (or Y2_SPT) call begins while the unit was under “Y1 cooling” control, compressor no. 2 will not be started until “Y1 cooling” control has ended.
If the Y2 (or Y2_SPT) call ends, with compressor 1 in an unloaded state and compressor 2 ON, then compressor 1 will be immediately brought up to the fully loaded state. If however, the Y2 (or Y2_SPT) call ends, with compressor 1 in an unload- ed state and compressor 2 OFF, then compressor 1 will be left in its unloaded state. In either case the compressor 1 will be loaded/unloaded as appropriate to the “Y1 Low Limit”.
The control shall lockout compressors if SAT becomes too low and an alarm shall be issued.
Compressor no. 1 lockout at SAT < 53 F. Compressor no. 2 lockout at SAT < 48 F.
If SAT sensor fails the control will energize compressor no. 1 fully loaded (unloaders off), whenever there is a Y1 (or Y1_SPT) call. Compressor no. 2 will be energized whenever there is a call for Y2 (or Y2_SPT).
NOTE: When a VAV unit with software version 4.0 and later is configured to operate from a space thermostat (VVT® relay pack) or a space sensor, compressors start loaded and then unload as needed. This is the opposite of the normal VAV unloading sequence. When operating from
FIELD TEST — The field test program is initiated by moving up DIP switch no. 4 to the OPEN position. The
If the unit is equipped with power exhaust, stage 1 will be energized for 5 seconds. If the unit is configured for stage 2 of power exhaust, stage 2 will be energized for 5 seconds after the first stage is deenergized.
The first stage of heat will be energized for 30 seconds, after which the second stage heat will be energized for an additional 30 seconds. Heat is then deenergized.
The last step is the Cooling mode.
The compressors will now deenergize, followed by the out-
The field test is then complete.
SERVICE
Before performing service or maintenance operations on unit, turn off main power switch to unit. Electrical shock could cause personal injury.
Service Access — All unit components can be reached through clearly labelled hinged access doors. These doors are not equipped with tiebacks, so if heavy duty servicing is need- ed, either remove them or prop them open to prevent accidental closure.
Each door is held closed with 3 latches. The latches are se- cured 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 ori- entation and position of the top cover be marked on the unit prior to disassembly. This will allow proper replacement 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 so can result in water leakage into the evaporator section of the unit.
Cleaning — Inspect unit interior at beginning of each heat- ing and cooling season and as operating conditions require. Remove unit side panels and/or open doors for access to unit interior.
MAIN BURNERS — At the beginning of each heating sea- son, inspect for deterioration or blockage due to corrosion or other causes. Observe the main burner flames and adjust if nec- essary. Check spark gap. See Fig. 64. Refer to Main Burners section on page 94.
FLUE GAS PASSAGEWAYS — The flue collector box and heat exchanger cells may be inspected by removing gas section access panel (Fig.
Fig. 63 — Door Latch
Fig. 64 — Spark Gap Adjustment
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