12
McQuay IM 987
Introduction
Controls, Settings, and Functions
Table 2
below lists all of the unit control devices and
associated information.
Table 2: Controls, Settings, and Functions
Symbol
Description
Function
Reset
Location
Setting
Range
Differential
Part no.
DAT
Discharge air
temperature
sensor
Senses discharge air
temperature
N/A
Discharge air
section
N/A
N/A
060004705
DHL
Duct high limit
switch
Prevents excessive VAV
duct pressures; shuts off fan
Auto
Main control
panel
3.5" w.c
(871.8 Pa)
0.05–5.0" wc
(12.5–1245.4
Pa)
.05" wc
(12.5 Pa),
fixed
065493801
EFT
Entering fan air
temperature
sensor
Senses entering fan air
temperature
N/A
Inlet of supply
fan
N/A
N/A
060004705
FP1, 2
Evaporator frost
protection
Senses low refrigerant
temperature
N/A
Return bends
of evaporative
coil
Opens at
30°F
Closes at
45°F
N/A
N/A
072501901
FS1
Freezestat
Shuts off fans, opens heating
valve, and closes outdoor
damper if low air
temperature at coil is
detected
Auto
Heating
section
38°F (3°C)
or as
required
35°F–45°F
(2°C–7°C)
12°F (7°C),
fixed
072502001
MCB
Main control
board
Processes input information
N/A
Main control
box
N/A
N/A
N/A
060006101
OAE
Enthalpy control
(electro-
mechanical)
Returns outside air dampers
to minimum position when
enthalpy is too high
Auto
Economizer
section
“B” or as
required
A–D
Temperature:
3.5°F (2°C)
Humidity:
5% fixed
030706702
Enthalpy control
(electronic)
Returns outside air dampers
to minimum position when
outside air enthalpy is higher
than return air empalthy (use
RAE)
Auto
Economizer
section
Fully CW
past “D”
(when used
with RAE)
A–D
N/A
049262201
OAT
Outside air
temperature
sensor
Senses outside air
temperature
N/A
N/A
N/A
060004705
PC5
Dirty filter switch
Senses filter pressure drop
Auto
First filter
section
As required
.05-5" wc
(12.5–1245.4
Pa)
.05" wc
(12.5 Pa)
065493801
PC6
Dirty filter switch
Senses filter pressure drop
Auto
Final filter
section
As required
.05-5" wc
(12.5–1245.4
Pa)
.05" wc
(12.5 Pa)
065493801
PC7
Airflow proving
switch
Senses supply fan pressure
to prove airflow
Auto
Supply fan
section
.10" wc (25
Pa)
.03-1.40" wc
(7.5–348 Pa)
.03" wc
(7.5 Pa), fixed
060015801
RAE
Return air
enthalpy sensor
Used to compare return air
enthalpy to outside air
enthalpy (used with OAE)
N/A
Economizer
section
N/A
N/A
N/A
049262202
RAT
Return air
temperature
sensor
Senses return air
temperature
N/A
Return air
section
N/A
N/A
060004705
SD1
Smoke detector,
supply air
Initiates unit shutdown if
smoke is detected
Manual
Discharge air
section
N/A
N/A
N/A
04925001
SD2
Smoke detector,
return air
Initiates unit shutdown if
smoke is detected
Manual
Return air
section
N/A
N/A
N/A
04925001
SPS1
Static pressure
sensor duct #1
Converts static pressure
signals to voltage signals
N/A
Main control
box
N/A
0–5" wc
(0–1245.4 Pa)
1–6 V (dc) out
N/A
049545007
