Thomas & Betts RZ405 Combustion Air Proving Switch, Blower Motor and Drive, Transformer, Module

Venter

Pressure Switch

Transformer	Gas
	Valve
Terminal Strip
Ignition Control	Contactors
Module

Figure 15 - Control

Locations

Limit Control

Supply Wiring Terminal Block (behind the gas valve)

(Line voltage enters the control compartment through a hole in the top of the heater cabinet.)

Thermostat Terminal Strip (Thermostat wires enter the control compartment through a hole in the right side of the heater cabinet.)

13. Combustion Air Proving Switch

The combustion air proving switch is a pressure sensitive switch that monitors air pressure to ensure that proper combustion air is available.

The switch is single pole/double throw with the normally open contacts closing when the proper airflow is sensed in the system.

On start-up when the heater is cold, the sensing pressure is at the most negative level, and as the heater and flue system warm up, the sensing pressure becomes less negative. After the system has reached equilibrium (about 20 minutes), the sensing pressure levels off.

If a restriction or excessive flue length or turns cause the sensing pressure to be outside the switch setpoint, the pressure switch will function to shut off the main burners. The main burners will remain off until the system has cooled and/or the flue system resistance is reduced. The table below lists the approximate water column nega- tive pressure readings and switch setpoints for sea level operating conditions.

Model Start-Up Equilibrium			Set Point	Set Point
Size	Cold		“OFF”	“ON”
150	1.45	1.05	.75	.90
200	1.50	1.05	.75	.90
250	1.55	1.10	.75	.90
300	1.60	1.15	.75	.90
350	1.30	1.05	.75	.90
400	1.20	1.00	.75	.90

DANGER: Safe operation of this unit requires proper venting flow. NEVER bypass the com- bustion air proving switch or attempt to operate the unit without the venter running and the proper flow in the vent system. Hazardous conditions could result. See Hazard Levels, page 2.

14. Blower Motor and Drive

Model CAUA units are equipped with either direct drive motor(s) and blower(s) or adjustable belt-drive blower(s) and motor.

Direct Drive

All direct drive blower motors are 1 horsepower. Sizes 150-200 have a single motor. Size 150 has a 12-9 blower; Size 200 has a 12-12 blower. Sizes 250-400 have dual motors with dual 12-9 blowers.

Belt Drive

The motor horsepower on a belt drive unit is whatever was specified on the order ranging in size from 1/4 HP to 5 HP. Check the heater rating plate and the motor rating plate.

As part of the start-up procedure, check belt tension. Proper belt tension is important to the long life of the belt and motor. A loose belt will cause wear and slippage. Too much tension will cause excessive motor and blower bearing wear. Adjust the belt tension by turning the adjusting screw on the motor base until the belt can be depressed 3/4". (See Figure 16.) After correct tension is achieved, re-tighten the locknut on the adjustment screw. Be sure that the belt is aligned in the pulleys.

Figure 16 -

Check Belt

Tension 3/4” (19mm)

Most blower motors are equipped with thermal overload protection of the automatic, reset type. If the motor is not equipped with thermal overload protection, the unit will be equipped with a starter. The adjustable setting on the starter will be factory set to match the amp draw of the motor and sealed. No change should be made to the starter setting unless the original motor is replaced. Starters are equipped with a manual reset. If an overload condition is experienced, the condition must be corrected and the starter must be manually reset.

After the installation is complete including all ductwork, the amp draw of the motor should be checked with an amp meter to verify that the motor amp rating on the motor nameplate is not being exceeded. Amps may be adjusted downward by reducing the blower speed or by increasing the duct system static pressure. The temperature rise must be within the range specified on the unit rating plate.

Mfg No. 164771, Page 15