Modulation Motors

Page �

Figure1. Honeywell mod motor M7284C-1000 installed on heater.

Troubleshooting modulation motorsPurposeThis document provides a guide for troubleshoot-ing burner modulation motors (Figure 1), which are commonly called mod motors. They are also known as modulation actuators.

ScopeThis document applies to Honeywell mod motors M7284C-�000, M9�74C-�025, and M9�84F-�034 used on Heatec HC and HCS heaters.

What the mod motor doesThe mod motor is connected to mechanical linkage that opens and closes fuel valves and air dampers of the burner (Figure 1). It provides proportional control of its firing rate. The shaft of the mod

motor operates the linkage as it rotates within an arc of 90 degrees.

Key components of concern• Low-fire cam and low-fire proof switch.• High-fire cam and high-fire proof switch. • Resistor board or resistor harness.• Transformer.

NOTICE: For clarity some photos of mod motor are shown not installed on the heater. It is not necessary to remove it to perform the checks and adjustments described.

HEATEC TEC-NOTEPublication No. 1-07-184 Revised 4-24-07

LINKAGE

MOD MOTOR

LINKAGE

SHAFT

Key differencesHoneywell mod motors

M7284C-1000 M9174C-1025 M9184F-1034

Heatec heaters used onHC & HCS

12-06 & after HC & HCS

prior to 12-06

HC & HCSearly units with

modulating burners

Color of low-fire cam Red Blue Red

Wiring of low-fire proof switch Normally closedNormally open(held closed)

Normally closed

Wires used, low-fire proof switchRed=commonYellow=Normally closed

Red=commonYellow=Normally open

Red=commonYellow=Normally closed

Color of high-fire cam Blue Blue Blue

Wiring of high-fire proof switch Normally open Normally open Normally open

Wires used, high-fire proof switchBlack/red=commonBlack/blue=Normally open

Black/red=commonBlack/blue=Normally open

Black/red=commonBlack/blue=Normally open

Resistor board or resistor harness (Not used) Yes Yes

Figure 2. Top view of Honeywell mod motor M7284C-1000.

LOW-FIRECAM (RED)

LOW-FIREPROOF SWITCH

HIGH-FIRECAM (BLUE)

HIGH-FIREPROOF SWITCH

TRANSFORMER120 VAC TO 24 VAC

Model differencesThe following table identifies the models of mod motors used on Heatec HC and HCS heaters that

have modulating burners. There are important differences in the way the switches and cams are configured. Figure 2 shows the motor now used.

Publication No. 1-07-184

TERMINAL BOARD

Interaction with Fireye flame monitor (Figure 3) The Fireye flame monitor monitors the open/closed status of the low-fire and high-fire proof switches in the mod motor while the burner is being purged. The low-fire proof switch is wired between terminals m and d. The high-fire proof switch is wired between terminals d and 8. Thus, the flame monitor shows either m-d limit or d-8 limit when indicating the status of these switches. Each switch is activated and de-deactivated by its own rotating cam in the mod motor.

• On mod motors with a red low-fire cam the low-fire proof switch remains in its normally closed position while the damper is fully closed. After the damper begins to open, the cam opens the switch.

• On mod motors with a blue low-fire cam the cam holds the low-fire proof switch in its closed position while the damper is fully closed. After the damper begins to open, the cam opens the switch.

• On all mod motors, the high-fire cam closes the high-fire proof switch when the damper reaches a preset open position. After the damper begins to close, the cam opens the switch.

Figure 3. Fireye flame monitor.

SCRL MODERESET

FLAME-MONITOR

AUTOFLAME SIGNAL

40


SHOCK HAZARD. High voltage is present on certain terminals and wires inside the main control panel, inside the mod motor and inside the burner panel. Touching them will cause death or serious injury.

Do not work on these components unless you are a qualified technician familar with the hazards of electricity.

Some circuits in the main control panel may receive power from remote sources. Thus, the breaker operator on the door may not deenergize all exposed live parts.

Always use a voltage tester to make sure there is no voltage on the terminals or bare wires you may touch.

Interaction with Honeywell modulation controller (Figure 4)The modulation controller controls the mod motor using a circuit that provides an output of 4 to 20 mA. With a 4 mA signal the mod motor should be in the low-fire position with the damper fully closed. With a 20 mA signal the mod motor should open the damper to the high-fire position.

Figure 4. Honeywell modulation controller.

A common problemFaulty electrical connections are common causes of mod motor malfunctions. Faulty connections can be caused from loose connections, dust, or corrosion from moisture. Connection problems may occur at the following locations:

• Terminals in mod motor. (Figure 5)

• Terminals on Temperature controller (Figure 6).

• Terminal strip on back plate of heater panel (Figure 7).

• Terminal strip in burner junction box (Figure 8).

Other problems• Failure of resistor board or resistor harness

(Figures 11 and 12).• Slippage of cams (Figure 2).

• Failure of transformer (Figure 2).

Figure 5. Terminal connections in mod motor.

Figure 6. Terminal connections on Honeywell modulation controller.

Figure 7. Terminal connections on back plate of heater panel.


Figure 8. Terminal connections in burner junction box.

Symptoms of problems• Mod motor fails to move when burner is first

turned on.• Flame monitor (Figure 3) indicates abnormal

status of either m-d limit or d-8 limit.• Mod motor fails to operate the linkage.• Modulation controller (Figure 4) fails to

modulate the mod motor.

Remedy for faulty electrical connectionsAll wire connections that pertain to the mod motor have either screw terminals or cage-clamp spring terminals. (See Figures 5, 6, 7 and 8) On connections with screw terminals use a screwdriver to slightly loosen the screws and retighten them. On connections with cage clamps, push on the wire, wiggle it and then pull on it to make sure it is held tightly.

Figure 9. Using screwdriver to position cams.

Checking and resetting cams�. Remove the top cover so that you can gain

access to the tops of the cams (Figure 2).

2. Make sure the shaft of the mod motor is rotated to its position for a fully closed damper.

3. Check positions of the target lobes of the cams. The cams have click stops that hold them in position. Repositioning a cam does not turn the drive shaft of the mod motor.

4. You may be able to rotate the cams with your fingers. Otherwise insert the blade of a screwdriver in the slots of the cam (Figure 9) and rotate them.

5. In order to make sure the cams are positioned properly you may need to rotate them until you can see their target lobes (indicated by yellow dots in Figure 10) and then reset them to their proper positions. NOTE: The yellow dots are only shown in Figure �0. There are no dots on the actual lobes.

6. You can also use the blade of a small screwdriver to press on the actuating arms of the switches to determine whether they are actuated. All switches except the blue low-fire switch should not be actuated while the damper is closed. Thus you should hear a distinct click if you press on their actuating arms.

7. Because the blue low-fire switch should be actuated or held closed by the cam when the damper is closed, you should not be able to move its actuating arm. Note that it is shown with its arm in the actuated position in Figure 10.

8. Make sure the target lobes of the two cams are rotated to the positions shown relative to the actuating arms of the two switches as shown in Figure 10. The U-shaped ends of the switch arms should rest on the cams as shown in Figure 10.


12

Shielded Pair #2

Black

Red

White

Honeywell Modulating Motor

4–20 mA Signal Modulation Circuit

(14) (13)

Burner Control Relay

Jumper

White

Red

Alarm-2

ShieldedPair #1

Honeywell Controller UDC2500Thermocouple

Type J Duplex

Circuit Breaker

White

Red

Set at 20 degrees above setpoint.

1 A

Alarm-1

4–20mA SignalRed

White

HOLD NORMALLOW FIRE HOLD

–

27 25

+

19

+

26

–

21

5 6

8

L1

9

GND L2

13

+

–

12

1210

11 X9 11 13

10

T1 T224 vac

120 vac

14

12

16

15

Shield

Gnd Shld

Gnd

8

S-1

CB-4

BC 1

+

–

F

+

–

MODULATING MOTOR M7284C-1000

LEGENDDenotes terminal on Fireye Flame Monitor.

Denotes terminal on Modulating Controller.

Denotes terminal on terminal strip in control panel.

21

OptionalAuxiliary Output To Chatterbox

Figure 9A. Wiring diagram for mod motor currently used.

HONEYWELL MODELS M7284C-1000 AND MF9184F-1034

HONEYWELL MODEL M9174C-1025

LOW-FIRE CAM (RED)DAMPER CLOSED

LOW-FIRE CAM (BLUE)DAMPER CLOSED

HIGH-FIRE CAM (BLUE)DAMPER CLOSED

HIGH-FIRE CAM (BLUE)DAMPER CLOSED

BLK/RED(COMMON)

BLK/RED(COMMON)

RED(COMMON)

RED(COMMON)

YELLOW (NC)

YELLOW (NO) BLK/BLUE (NO)

BLK/BLUE (NO)

BLK/YELLOW (NC)

BLK/YELLOW (NC)BLUE (NO)

BLUE (NC)

90°

90°

90°

90°LOW-FIRE

CAM


(NORMALLY CLOSED

HIGH-FIRECAM

SHAFT


(NORMALLY OPEN)

LOW-FIRE CAM


(NORMALLY OPENBUT HELD CLOSED)

HIGH-FIRECAM

TOP VIEW

TOP VIEW

SHAFT


(NORMALLY OPEN)

YELLOW DOTS INDICATETARGET LOBES. CAMS ROTATE CLOCKWISE AS DAMPER OPENS.

YELLOW DOTS INDICATETARGET LOBES. CAMS ROTATE CLOCKWISE AS DAMPER OPENS.

Figure10. Configuration of cams and switches.


Checking transformer in the mod motor�. Make sure heater control switch is set to

off. 2. Make sure there is �20 Vac on the primary

winding of the transformer using an ac voltmeter. Check for 24 Vac on its secondary winding. The transformer is defective if there is no voltage on its secondary winding.

Checking resistor board and motor (Fig. 11)�. Make sure heater control switch is set to

off.

2. Make sure that the dipswitch settings are correct as indicated in Figure 11. Use a ballpoint pen to make sure that switches are fully depressed. (Partially depressed switches have been a problem in the past.)

3. Make sure its transformer is not defective. Refer to instructions above.

Figure11. Resistor board, Heatec PN 5004718, Honeywell PN 221508A.

4. Disconnect wires from terminals r, w and b of the resistor board.

5. Temporarily connect a short jumper wire from terminals r to b. The motor of the actuator should go to high-fire, which indicates that the motor is okay and its particular circuit on the resistor board is okay. Otherwise, either the motor or the resistor board is bad.

6. Temporarily connect a short jumper wire from terminals w to r. The motor of the actuator should go to low-fire (if it is not already there), which indicates that the motor is okay and its particular circuit on the resistor board is okay. Otherwise, either the motor or the resistor board is defective and should be replaced.

7. Remove the resistor board.

8. Connect the two wires from the secondary side of the transformer to terminals t1 and t2 of the circuit board where the resistor board was removed.

DIP SWITCHES


SWITCH IS OPEN WHEN BLUE BAR APPEARS NEXT TO SWITCH NUMBER

DIP SWITCH SETTINGS1 2 3 4 5 6 7 8 9 10

OPEN OPEN OPEN OPEN CLOSED CLOSED OPEN CLOSED OPEN OPEN

9. Using a short jumper wire, temporarily connect from terminal r to b on the circuit board. If the motor works, the resistor board is defective and should be replaced.

Replacing mod motorThe Model M7284C-�000 Honeywell motor replaces all inoperable mod motors used on past and present Heatec HC and HCS heaters with modulating burner. Do not use a resistor harness or resistor board (Figures 11 and 12) with this motor.

Be sure to use the new wires that come with the new mod motor (Figure 13) and connect directly to the low-fire and high-fire switches. Do not use the old wires. Although the old wire colors may be the same as the new wires they may not be connected to the same terminals on the low-fire and high-fire switches.

See wiring diagram (Figure 9A) and cover of mod motor (Figure 14) for wiring information. Note differences in terminal markings indicated below:

TERMINAL MARKINGS IN MOD MOTORS

M7284C-1000M9174C-1025M9184F-1034

+ W

– R

F B

Figure 13. Wires furnished with Model M7284C-1000 Honeywell mod motor.

Figure 14. Information in cover of mod motor. Figure 12. Resistor kit (harness), Heatec PN 5018099, Honey-well PN 4074EDC.

Heatec, Inc. 5200 Wilson Road Chattanooga, Tennessee 37410 www.heatec.com (423) 821-5200 (800) 235-5200 Fax (423) 821-7673

66.5 OHM RESISTOR

237 OHM RESISTOR

NOTE: Special precision resistors are used. Do not use substitutes

Publication No. 1-07-184 © 2007 Heatec, Inc.

Modulation Motors

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