HEATEC TEC-NOTE. Troubleshooting modulation motors

Transcription

1 HEATEC TEC-NOTE Revised Troubleshooting modulation motors Purpose This document provides a guide for troubleshooting burner modulation motors (Figure 1), which are commonly called mod motors. They are also known as modulation actuators. Scope This document applies to Honeywell mod motors M7284C-1000, M9174C-1025, and M9184F-1034 used on Heatec HC and HCS heaters. What the mod motor does The 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. SHAFT MOD MOTOR LINKAGE LINKAGE Figure1. Honeywell mod motor M7284C-1000 installed on heater. Page

2 TRANSFORMER 120 VAC TO 24 VAC CAM (BLUE) CAM (RED) TERMINAL BOARD Figure 2. Top view of Honeywell mod motor M7284C Model differences The 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. Key differences Heatec heaters used on Honeywell mod motors M7284C-1000 M9174C-1025 M9184F-1034 HC & HCS & after HC & HCS prior to HC & HCS early units with modulating burners Color of low-fire cam Red Blue Red Wiring of low-fire proof switch Normally closed Normally open (held closed) Normally closed Wires used, low-fire proof switch Red=common Yellow=Normally closed Red=common Yellow=Normally open Red=common Yellow=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 switch Black/red=common Black/blue=Normally open Black/red=common Black/blue=Normally open Black/red=common Black/blue=Normally open Resistor board or resistor harness (Not used) Yes Yes Page 2

3 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. 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 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. SCRL Figure 3. Fireye flame monitor. AUTO 40 FLAME SIGNAL RESET MODE FLAME-MONITOR 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. Page 3

4 A common problem Faulty 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). 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 connections All wire connections that pertain to the mod motor have either screw terminals or cageclamp 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 5. Terminal connections in mod motor. Figure 7. Terminal connections on back plate of heater panel. Figure 6. Terminal connections on Honeywell modulation controller. Figure 8. Terminal connections in burner junction box. Page 4

5 Checking and resetting cams 1. 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. Figure 9. Using screwdriver to position cams. 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 10. 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 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 MODULATING MOTOR M7284C Figure 9A. Wiring diagram for mod motor currently used. Thermocouple Type J Duplex Circuit Breaker CB-4 Honeywell Controller UDC Jumper Alarm-2 White Red Gnd Shielded Pair # LOW FIRE HOLD HOLD NORMAL Shielded Pair #2 S Shld ma Signal Modulation Circuit X 10 White Red Black F 120 vac T1 T2 24 vac Honeywell Modulating Motor 1 A 8 L1 8 GND Alarm-1 L2 9 Set at 20 degrees above setpoint. 14 Burner Control Relay (14) (13) BC Gnd White 15 Red 16 Shield White Optional Auxiliary Output To Chatterbox Red 420mA Signal LEGEND Denotes terminal on Fireye Flame Monitor. Denotes terminal on Modulating Controller. Denotes terminal on terminal strip in control panel. Page 5

6 HONEYWELL MODELS M7284C-1000 AND MF9184F-1034 BLUE (NO) YELLOW (NC) BLK/YELLOW (NC) BLK/BLUE (NO) RED (COMMON) (NORMALLY CLOSED TOP VIEW CAM (NORMALLY OPEN) BLK/RED (COMMON) CAM SHAFT YELLOW DOTS INDICATE TARGET LOBES. CAMS ROTATE CLOCKWISE AS DAMPER OPENS. CAM (RED) DAMPER CLOSED CAM (BLUE) DAMPER CLOSED HONEYWELL MODEL M9174C-1025 BLUE (NC) YELLOW (NO) BLK/YELLOW (NC) BLK/BLUE (NO) RED (COMMON) (NORMALLY OPEN BUT HELD CLOSED) TOP VIEW CAM BLK/RED (COMMON) (NORMALLY OPEN) CAM SHAFT CAM (BLUE) DAMPER CLOSED Figure10. Configuration of cams and switches. YELLOW DOTS INDICATE TARGET LOBES. CAMS ROTATE CLOCKWISE AS DAMPER OPENS. Page 6 CAM (BLUE) DAMPER CLOSED

7 Checking transformer in the mod motor 1. Make sure heater control switch is set to off. 2. Make sure there is 120 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) 1. 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. 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 SWITCH SETTINGS OPEN OPEN OPEN OPEN CLOSED CLOSED OPEN CLOSED OPEN OPEN SWITCH IS OPEN WHEN BLUE BAR APPEARS NEXT TO SWITCH NUMBER DIP SWITCHES Figure11. Resistor board, Heatec PN , Honeywell PN A. Page 7

8 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 motor The Model M7284C-1000 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: Figure 13. Wires furnished with Model M7284C-1000 Honeywell mod motor. TERMINAL MARKINGS IN MOD MOTORS M7284C-1000 M9174C-1025 M9184F-1034 W R F B 66.5 OHM RESISTOR 237 OHM RESISTOR NOTE: Special precision resistors are used. Do not use substitutes Figure 12. Resistor kit (harness), Heatec PN , Honeywell PN 4074EDC. Figure 14. Information in cover of mod motor. Heatec, Inc Wilson Road Chattanooga, Tennessee (423) (800) Fax (423) Page Heatec, Inc.