9. Controls
The main operating gas valve is powered by the 24-volt control circuit
through the thermostat and safety controls. The main control valve is a dia-
phragm type providing regulated gas flow preset at the factory. (For loca
-
tion, see
FIGURE 28
, page 43.)
WARNING: The operating valve is the prime safety shut
-
off. All gas supply lines must be free of dirt or scale before
connecting the unit to ensure positive closure. See Haz
-
ard Levels, page 2.
9.2 Gas Valve
9.3 Safety Controls
9.3.1 Combustion Air Proving (Pressure Switch)
The combustion air proving switch is a pressure sensitive switch that moni-
tors air pressure to ensure that proper combustion airflow is available. The
switch senses the differential pressure between the negative pressure in
the venter housing and the pressure in the cabinet. (For switch location,
see
FIGURE 28
, page 43.)
On startup when the heater is cold, the sensing pressure is at the most
negative level, and as the heater and vent 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 vent length or turns cause the sensing pressure
to be outside the switch setpoint, the pressure switch will function to shut-
off the main burner. The main burner will remain off until the system has
cooled and/or the flue system resistance is reduced.
The Table below lists the approximate water column differential pressure
readings and switch setpoints for sea level operating conditions for Model
UEAS heaters.
9.1
Thermostat
Use either an optional thermostat available with the heater or a field-sup
-
plied 24-volt thermostat. Install according to the thermostat manufacturer’s
instructions, paying particular attention to the requirements regarding the
location of the thermostat.
Make sure that the heat anticipator setting on the thermostat is 0.6 amps
(or in accordance with the amperage value noted on the wiring diagram of
your heater).
Make thermostat connections at the terminal strip on the back of the heater.
The strip has four terminals, G, W1, R, and W2; refer to the wiring dia
-
gram.
IMPORTANT:
All units MUST be operated by a 24-volt thermostat.
Never
use a line voltage disconnect switch as a means of operating the heater.
Multiple Heater Control, Option CL31 and Option CL32
-
If the heater
was ordered with a multiple heater control option, one thermostat can be
used to control up to six heaters. The option includes a 40VA transformer
that replaces the standard transformer in the “controlling” unit and a relay
assembly that attaches to the additional unit. Option CL31 provides for con-
trol of two heaters. If control of additional heaters is desired (up to six total),
Option CL32 which is the relay assembly only must be added to each addi-
tional heater.
The option packages are shipped separately and include complete instruc-
tions on installation and wiring.
Form I-UEAS, Page 32
