AMX VST Instruction Manual page 27

Thermostat Action Commands (Cont.)
Command
HVAC
Report HVAC Relay States
ViewStat Communicating Thermostat - Programming Protocol Reference Guide
Description
Thermostats control HVAC units by energizing various relays within the
thermostat completing a circuit to the HVAC controls. This command
reports the on or off state of each relay within the thermostat.
Syntax:
SN[address] HVAC?
Reply Format:
SN[address] HVAC=G±Y1±W1±Y2±W2±B±O± (see example below)
The relay names used are consistent with HVAC terminology. Note that the
compressor is active during cooling operation and during heating opera-
tion with heat pump systems:
• G: Fan
• Y1: First stage compressor or Dehumidifier
• W1: First stage heat (or auxiliary heat with heat pump systems) or
Humidifier
• W2: Second stage heat (or 2nd stage auxiliary heat during Emergency
Heat operation with heat pump systems)
• Y2: Second stage compressor
• O: Reversing valve cooling mode (heat pump)
• B: Reversing valve heating mode (heat pump)
On (or energized) is indicated by a plus sign "+" following the relay name.
Off is indicated by a minus sign "-" following the relay name. An example
of this command sequence is as follows:
Command:
SN1 HVAC?
(Request to the thermostat with network address 1 as to the state of the
HVAC control relays)
Response:
SN1 HVAC=G+Y1+W1-W2-Y2-O+B-
ViewStat responds that the fan and first stage compressor relays are
currently energized.
ViewStat Programming Protocol
23