Preliminary Circuit Analysis
In order to diagnose the cause of problems in this
system, it is necessary to determine certain values. It
is helpful to have an AC and DC voltmeter and an
ohmmeter capable of reading 0 to 15,000 ohms. For
ease in troubleshooting, it is necessary to rewire the
system, replacing the discharge air sensor with a
4500 ohm, ½ watt test resistor.
Modulating Function Test:
Connect a DC voltmeter to amplifier terminals 1 and
2. If more convenient, the meter may be attached to
the MR valve terminals. Rotate temperature selection
knob to maximum setting – the DC volts should read
zero. The voltage should gradually increase to at least
20 volts when the temperature selector is slowly
rotated to its minimum (generally over a 3
º
to 4
º
range).
Automatic Valve Function:
After the electronic modulation function is tested, a
voltage reading must be taken across the automatic
gas valve. These voltage readings will be
approximately 24 V AC with the temperature
selection knob at maximum setting, zero volts AC
with the selector at minimum setting. The relay
switching action should occur when the modulating
voltage is between 15 and 19V DC.
If these voltage readings are observed as noted, it is
proved that the amplifier and temperature selector are
operating properly.
After testing, remove the resistor and reconnect the
discharge air sensor.
Maintenance
1.
Motors should be relubricated according to the manufacturer’s lubrication instructions.
2.
Filters must be cleaned (cleanable type) or replaced (throw-away type) with like filters as often as necessary so
as not to restrict air delivery.
3.
Twice a year check belts and sheaves for alignment and belt tension.
4.
When a belt is replaced, shorten center distance between sheaves by loosening motor bolts and sliding motor
on support. On units requiring multiple belts, use a matched set.
5.
The following procedure is recommended for tensioning belts:
A.
Measure span length “X” shown in Figure I.
B.
At the center of span length “X”, apply a force perpendicular to the span and large enough to deflect belt
1/64” for each inch of span length.
Example – The required deflection for a 40” span would be 40/64” or 5/8”.
C. Compare the force applied with the values given in Table V. If force is between the minimum and maximum
range shown, the drive tension should be satisfactory. A force below the minimum value indicates an
undertensioned belt and a force that exceeds the maximum value indicates an overtensioned belt.
6.
Lubricate main fan bearing with a high grade lithium base grease. Perform at least every quarter (three months)
or schedule according to equipment use.
TABLE V
Deflection Force
Belt Cross Section
(marked on belt)
Motor Pulley Pitch
Diameter
Minimum Maximum
3.0” – 3.6”
2.62 lbs. 3.25
lbs.
3.8” – 4..8”
3 lbs.
4 lbs.
A
5.0”- 7.0”
3.25 lbs.
5 lbs.
3.4” – 4.2”
3 lbs.
5 lbs.
4.4” – 5.6”
4 lbs.
5.87 lbs.
B
5.8” – 8.6”
5.25 lbs. 7.87
lbs.
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