Sterling Plumbing SDRIOM-2 - Manual (Page 22)

22
PRELIMINARY CIRCUIT ANALYSIS - SYSTEM 14
For ease in troubleshooting, it is advisable to wire the
system as follows (this differs from the normal connection).
The Discharge Air Sensor is disconnected and replaced
with a 10,000 ohm,1/2 watt test resistor (terminals 3 and
4). If inlet air sensor is being used, disconnect and replace
with a jumper. On units where the Remote Temperature
Selector is located a considerable distance from the heater,
it may be advantageous to connect the selector at the
heater location.
Connect a DC volt meter (capable of reading 0-24V DC)
on the Modulator or Modulator-Regulator Valve terminals.
Set the temperature to the minimum dial setting. The DC
voltage should read 0 volts. The DC voltage should
gradually increase to at least 20 volts as you slowly rotate
the dial to the maximum dial setting. If these voltages are
obtained, the valve function can now be checked out.
The operation of the valve with regard to voltage is as
follows: from 0 volts to approximately 5 volts, the
modulating valve should be on bypass flow with the heater
operating on low or minimum fire. From approximately
5 volts to 15 volts DC, the valve should be performing its
modulating function and the heater should be firing at a
modulated flow rate between low and high fire, depending
on the voltage. Above approximately 15 volts DC, the
valve should be delivering full flow to the heater and the
unit should be on full fire. If the DC voltage is obtained
on the valve terminals, but the heater does not respond as
described, the problem can be isolated to the valve itself
or to the gas control manifold of the heater.
In the event proper voltages are obtained and the valve
responds correctly to these DC voltages, the problem
could well be in the wiring leading to the Discharge Air
Sensor itself. This should also be reviewed in the check
list.
If the proper voltages are not obtained when wired as
instructed, the problem can be isolated to the electronics
and this may once again be reviewed in the check list.
After test, remove the test resistor and reconnect the
Discharge Air Sensor to terminals 3 and 4. If Remote
Temperature Selector has been moved, return it to its
original position.
PRELIMINARY CIRCUIT ANALYSIS - SYSTEM 44
This Preliminary Circuit Analysis will provide identification
of faulty components, improper wiring or calibration, and
other difficulties when used with the tabulated
Troubleshooting Guide.
NOTE: All voltages and resistance readings are
approximate.
Section 1
1.
Wire the system per Figure 1.
2. Connect a DC voltmeter to amplifier terminals #6
and #7.
3. Turn the Test-Potentiometer to minimum resistance
(2,000 ohms). The DC voltage should read 0 volts.
4. Turn the Test-Potentiometer slowly to maximum
resistance (12,000 ohms). The DC voltage should
gradually increase to at least 18 volts.
If proper voltages are observed, continue on with
Section 2.
If proper voltages are not observed, the problem is
identified with the Amplifier, the 24-volt AC power
supply, or the circuit connected to terminals #6 and #7.
Section 2
1.
Turn power OFF. Wire system per Figure 2. Turn
power ON.
2. Turn Test-Potentiometer to minimum resistance.
Voltage should be 0 volts.
3. Turn Test-Potentiometer slowly to maximum resistance.
The DC voltage should gradually increase to at least
18 volts.
If proper voltages are observed in both Section 1 and
2, the amplifier is satisfactory.
If proper voltages are not observed, continue testing
to identify the difficulty. Faults may be identified with
the amplifier, the 24V power supply, or the circuit
connected to terminals #6 and #7.
Section 3
1.
Observe burner flames and/or burner pressure as
Test- Potentiometer is turned through full range.
NOTE: From 0-5 volts, heater should be at bypass
or low; 5-15 volts, heater should respond with vari-
ous input rates; beyond 15 volts, heater is at maxi-
mum input.
If proper operation is observed, continue procedure to
check operation of sensing and selecting components.
If proper operation is not observed, see Trouble-shoot-
ing Guide to test M and MR valves and connecting
wiring.