Maintenance troubleshooting

Figure M-T-1. Resistance temperature curve for the zone sensor, entering water temperature sensor, and discharge air sensor. Thermisitor = 10kΩ at 77°F.

Board switches are factory set based on unit control options. Figure M-T-2 shows a relay board detail. Additional information on switch settings follows.

Switch SW1: Controller Type

SW1 determines the unit control type. Position 1 indicates one of the following:

•generic field controller

•low-voltage fan speed switch

•Tracer ZN010

•Tracer ZN510

Position 2 indicates Tracer ZN520.

Switch SW2: Electric Heat

SW2 determines if the unit has electric heat.

Switch SW3: High-Speed Interlock

SW3 determines if the unit will have a safety-mandated “high-speed interlock” with electric heat. High-speed interlock ensures heat dissipates in a manner that

LED indicates power

interface to

Tracer ZN controller

configuration switches (factory pre-set)

connection to valve & piping sensor crossover harness

keeps the unit in a safe operating condition. SW3 configures the unit to actuate high-speed interlock if the first or second stage is on.

SW3 is a three-position slide switch that actuates high-speed interlock to operate with specific electric heat coils.

•Position 1: default position and for low vertical units with electric heat

•Position 2: single-stage electric heat, model number digit 18 = N

•Position 3: two-stage electric

Switch SW4: Electric Heat Lockout SW4 allows the unit to use the electric heat lockout function when hydronic heat is in operation. Electric heat lockout prevents electric heat from enabling when hydronic heating is available. This

Do not adjust these

	Note: HAZARDOUS voltage	switch positions because
	in dashed area of board!	switch positions because
	in dashed area of board!	it may result in a safety
		it may result in a safety
	Figure M-T-2. Relay board detail	hazard!
	Figure M-T-2. Relay board detail

feature is on models with both hydronic and electric heat. Low vertical models with electric heat, switch SW4 to position 2 (on).

Troubleshooting the Relay Board

The relay board serves as a common interface to all of the standard end devices, and has an LED that indicates power to the board. Factory switches are pre-set and locked in place with lock-tight. However, these seals can be broken if field-modifications are needed.

If the board needs replacement, the switches on the new board must be field- set in the same positions as the old board, as shown in the unit wiring diagram.

Note: SW3 and SW4 affect safety functionality, and they are factory secured. When replacing a board with SW3 and SW4, be sure to affix the switch positions with 3M 3764Q or equivalent.

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