McQuay IM 987
87
Unit Options
Field Output Signals
The following outputs may be available for field connections
to a suitable device.
VAV Box Signal/Fan Operation Signal
Digital Output #10 (MCB-DO10) may be selected as either the
Fan Operation output or the VAV output via the keypad. The
VAV/Fan Op selection can be selected by accessing the Unit
Setup menu in the Extended Menu section.
Fan Operation
The Fan Operation Output (MCB-DO10) supplies 24 V (ac) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (ac) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (ac) is supplied from the T3
control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.
The Fan Operation output is on when the unit is not Off and
when both the unit is Off and airflow is detected. It is off when
the unit is off and airflow is not detected.
VAV Box Output
The VAV Box Output (MCB-DO10) supplies 24 V (ac) to
terminal 116 on the field terminal block (TB2) when the output
is on. To use this signal, wire the coil of a field supplied and
installed 24 V (ac) pilot relay across terminals 116 and 117 on
TB2. When this output is on, 24 V (ac) is supplied from the T3
control transformer through the output relay to energize the
field relay. Refer to the as-built wiring diagrams.
In the Heating state, the VAV Output is turned off to indicate
that hot air instead of the normal cool air is being supplied to
the VAV boxes. The VAV boxes are driven to their Heating
Position when hot air is provided based on either the normally
open or normally closed contacts of the VAV output. The VFD
will continue to be controlled to maintain the desired duct
static pressure. This output is also off when the unit is in the
Startup or Recirculation states. If this output is in the Heat (off)
position when the unit enters the Fan Only state or Minimum
DAT Control state, the output remains off for an adjustable
Post Heat Time (while the unit VFDs are driven to minimum
speed) or until the VFD gets to its minimum speed if the Post
Heat Time is set greater than 0. The Post Heat Timer can be
adjusted via the keypad/display Timer Setting menu in the
Extended Menus.
During unoccupied operation, the VAV Box Output is in the
Cool (on) position unless airflow is detected. When airflow is
detected, it switches to the Heat (off) position.
Figure 97: Field Output Schematic
Entering Fan Temperature Sensor
The entering fan temperature (EFT) sensor and an associated
“Lo Airflow Problem” alarm are provided on VAV units with
MicroTech III control and gas or electric heat. The EFT sensor
is located in the supply fan section of the unit at the supply air
funnel.
Heat is disabled whenever the airflow is detected to be too low
for safe heating operation. This condition is indicated when the
supply air temperature exceeds the mixed air temperature by
more than 60°F (16°C).
Note:
This value is not always 60°F. It depends on whether the
unit is gas or electric heat and on the burner/baffling
arrangement on gas heat units.
In this case, a “Lo Airflow Problem” alarm is generated and
heat is not enabled until the alarm is manually cleared. Refer to
the operation manual supplied with the unit for information
clearing alarms (OM 920).
Содержание RAH 047C
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Страница 74: ...74 McQuay IM 987 Wiring Diagrams Figure 82 VFD Control SAF and RAF Schematic continues on next page ...
Страница 104: ...104 McQuay IM 987 Final Control Settings Figure 117 Keypad Accessible Menu Structure ...
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