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PRELIMINARY CIRCUIT ANALYSIS – SYSTEM 14
For ease in troubleshooting, it is advisable to wire the
system as follows (this differs from the normal connec-
tion). 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 consid-
erable distance from the heater, it may be advanta-
geous 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 ap-
proximately 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 upon 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 de-
scribed, 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 or 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 electron-
ics 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 identifica-
tion of faulty components, improper wiring or calibra-
tion, 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 resis-
tance. (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
various input rates; beyond 15 volts, heater is at
maximum input.
If proper operation is observed, continue procedure
to check operation of sensing and selecting
components.
If proper operation is not observed, see Trouble-
shooting Guide to test M or MR valves and con-
necting wiring.
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