Honeywell m7415 User Manual

19

63-2484—2

7. If all minimum and maximum position adjustments are 

complete, remove the T-T1 jumper and reconnect the 

mixed air sensor.

(T

 × OA)+(T

 × RA)= T

Where:

T

O

 = Outdoor air temperature

OA = Percent of outdoor air

T

R

 = Return air temperature

RA = Percent of return air

T

M

 = Resulting mixed air temperature

NOTE: The following sample calculation uses only Fahren-

heit temperature.

EXAMPLE: Assume local codes require 10% outdoor air dur-

ing occupied conditions, outdoor air is 60°F and 

return air is 75°F. Under these conditions, what is 

the temperature of the mixed air?

(0.1 × 60°F)+(0.9 × 75°F)=6.0°F + 67.5°F=73.5°F

Mixed air will be 73.5°F when OA is 60°F and RA is 75°F with 

10 percent outdoor air entering the building.

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.

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 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.

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 external 

line voltage contactor is required to operate the 

exhaust fan.

—

When the exhaust fan is deactivated the EF and 

EF1 contacts open immediately.

Tables 6 through 10 provide step-by-step economizer checkout 

and troubleshooting steps. See Fig. 23 and 25 for enthalpy 

setpoint potentiometer, minimum position potentiometer and 

LED locations.

1

1

2

2

M9097

ENTHALPY CHANGEOVER

SETPOINT

LED LIGHTS WHEN

OUTDOOR AIR IS SUITABLE 

FOR FREE COOLING

INSERT DC MILLIAMMETER BETWEEN SO AND S FOR CHECKOUT 

AND TROUBLESHOOTING.

JUMPER USED FOR SINGLE ENTHALPY CONTROL.

TR

TR1

A

B

C

D

SO

SR

+

+

+

620 OHM

JUMPER

DC 

MILLIAMMETER

S

+