Emerson DH Manuel D’Utilisation

Use this section in troubleshooting your unit. Also refer to 6.0 - Alarm Descriptions and Solu-

tions. Suggestions are grouped by product function for convenience.  

Only qualified personnel should perform service on these units. Lethal voltage is present in 

some circuits. Use caution when troubleshooting with power on. Disconnect and lock out 

power before replacing components. Use caution and standard procedures when working with 

pressurized pipes and tubes.

When using jumpers for troubleshooting, always remove jumpers when maintenance is 

complete. Jumpers left connected could override controls and cause equipment damage.

Blower will not start

No main power

Check L1, L2 and L3 for rated voltage.

Blown fuse or tripped circuit 

breaker (CB)

Check fuses or CBs to main fan.

Overloads tripped

Push reset button on main fan overload. Check amp. draw.

No output voltage from 

transformer

Check for 24 VAC between P24-2 and P24-1. If no voltage, 

check primary voltage.

Control fuse blown or circuit 

breaker tripped

Check for 24 VAC between P4-4 and E1. If no voltage, 

check for short. Replace fuse or reset circuit breaker.

Start switch SS not making 

contact (SM only)

Jumper P9-1 to P9-2. Unit should start. If unit stops after 

jumper is removed, replace S1.

Blower runs but controls 

will not operate

Relay R1 not making contact 

(standard controls only)

Check for 24 VAC between P36-9 and P36-10. If voltage is 

not present, R1 is not receiving power.
Check air switch. Jumper P36-4 to P36-7 If R1 closes, air 

switch is not closing (check for blower rotation, loose wiring, 

and pinched tubing.) Remove jumper.
Check for 24 VAC at R1 coil. If the voltage is present and R1 

is not pulling, replace R1.

Actuator Motors

No 24 VAC power to motor

Check for 24 VAC between P22-3 and P22-5 (open), or P22-

1 and P22-5 (closed).

Chilled water or hot 

water/steam valve not 

opening

Motor operates but valve won’t 

open

Check linkage for adjustment and be sure that it is tight on 

the valve.

Modulating Motors

No 24 VAC power to motor

Check linkage for adjustment and be sure that it is tight on 

the valve.

No signal from control

Check DC voltage on printed circuit board in motor. Terminal 

No. 1 is grounded and No. 3 is positive. DC voltage should 

vary from 0.8 to 2.0 VDC or above as temperature control is 

varied below room temperature on cooling valve or above 

room temperature on heating valve.

Motor not working

Remove wires on terminal No. 1 and No. 3 from the motor 

(do not short). With 24 VAC power from TR to TR jumper 

terminal 1 and 2 on motor to drive open. Remove jumper to 

drive closed, if motor fails to work, replace it.