Checkout And Troubleshooting - Honeywell C7400 Manual

DCV Maximum Position Adjustment
1. Disconnect mixed air sensor from terminals T and T1
and short terminals T and T1.
2. Connect a jumper between terminals AQ and AQ1.
3. Connect 24 Vac across terminals TR and TR1.
4. Adjust the potentiometer on the face of the device with a
small screwdriver for desired maximum position.
5. If all minimum and maximum position adjustments are
complete, remove the T-T1 jumper and reconnect the
mixed air sensor.
Enthalpy Changeover Setpoint
Outdoor Enthalpy Changeover Setpoint
(Single Enthalpy)
The outdoor enthalpy changeover setpoint returns the outdoor
air damper to minimum position when enthalpy rises above its
setpoint. Enthalpy setpoint scale markings, located in the
device, are A, B, C and D. See Fig. 18 for the corresponding
control point. The factory-installed 620-ohm jumper must be in
place across terminals SR and SR+. Temperature and
humidity points to the left of the selected curve will allow the
dampers to open for free cooling.
Differential Enthalpy Changeover Setting
Differential enthalpy control uses two C7400 Enthalpy
Sensors connected to one logic module. The logic module
compares outdoor air to return air.
NOTE: Turn the enthalpy setpoint potentiometer fully clock-
wise to the D setting.
The logic module selects the lower enthalpy air (return or
outdoor) for cooling. For example, when outdoor air has lower
enthalpy than return air, the module calls to open the outdoor
air damper to bring in outdoor air for free cooling.
Exhaust Setpoint
The exhaust setpoint determines when the exhaust fan runs
based on damper position. When the exhaust fan call is
made, the module provides a 60 ±30 second delay before
exhaust fan activation. This delay allows the damper to reach
the appropriate position to avoid unnecessary fan overload.
NOTES:
— EF and EF1 are 24V dry contacts only. An exter-
nal line voltage contactor is required to operate
the exhaust fan.
— When the exhaust fan is deactivated the EF and
EF1 contacts open immediately.
CHECKOUT AND
TROUBLESHOOTING
Tables 6 through 10 provide step-by-step economizer
checkout and troubleshooting steps. See Fig. 25 and Fig. 28
for enthalpy setpoint potentiometer, minimum position
potentiometer and LED locations.
W7459
B
A
1 INSERT DC MILLIAMMETER BETWEEN S O AND S FOR CHECKOUT
AND TROUBLESHOOTING.
2
JUMPER USED FOR SINGLE ENTHALPY CONTROL.
Fig. 28. Meter location for checkout and troubleshooting.
21
SOLID STATE ECONOMIZER SYSTEM
ENTHALPY CHANGEOVER
SETPOINT
TR1
TR
C
1
+
S O
+
D
S R
+
2
620 OHM
JUMPER
LED LIGHTS WHEN
OUTDOOR AIR IS SUITABLE
FOR FREE COOLING
+
S
C7400
DC
MILLIAMMETER
M9097
63-2484—03