On MZVAV unit equipped with Staged Heat (electric or gas), the unit will not run in a discharge air heating mode. These units will only heat in a constant volume heating mode in the form of morning or daytime warmup.
Units equipped with modulating gas heat can be operated in discharge air heating control, but the unit will not switch over automatically. How it is manually switched depends on how the unit is being controlled, see below for BAS and Standalone methods.
BAS Controlled
BCI-R - The BAS will need to determine when discharge air heating is required and will need to switch MO-8 to "Heating" (state 2). When discharge air heating is no longer required, it is recommended that the BAS release the point back to "Auto" (state 1)
LCI-R - The BAS will need to determine when discharge air heating is required and will need to switch nviApplicMode to "HVAC_HEAT" (state 1). When discharge air heating is no longer required, it is recommended that the BAS release the point back to "HVAC_AUTO" (state 0)
Standalone Control
MZVAV unit are supplied with terminals for a manual changeover input. These terminals are located on LTB-20 & LTB 21. A closed contact across these two terminal indicates a request for changeover to discharge air heating control.
For more information on setting up the RTAM for standalone operation see:
VAV Quick Setup for Temporary Operation
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.