Aprilaire 1710A Troubleshooting Manual page 4

DO NOT MEASURE RESISTANCE OR DO A CONTINUITY CHECK OF THE HIGH
TEMPERATURE SWITCH WHILE THE SWITCH IS CONNECTED TO THE POWER BOARD
– DAMAGE TO THE CONTROL CAN OCCUR.
e. If the COMP LED is on but the compressor is not, measure the voltage at the COMP
BRWN and NTRL ORG terminals on the power board.
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If the high temperature switch is good, disconnect the ribbon cable (the
ON/OFF switch should be ON) from the control board and use a small piece of
solid (not stranded) wire, a paper clip or the leads of an ammeter to touch
together pads 4 and 7 on the ribbon cable.
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If the compressor turns on the control board will need to be replaced.
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If the compressor does not turn on, the power board will need to be
replaced.
If the voltage is 120VAC (nominal) then the problem lies with the run capacitor,
the connections at the compressor or the current limiting switch under the
compressor cap.
o Disconnect the wires connected run capacitor and the orange wire
connected to the power board. Measure the capacitance of the run
capacitor – it should be 55 microfarads ± 5% for the 1710A/1750A and 60
microfarads ± 5% for the 1770A. If not, replace the capacitor.
o Measure the resistance across the compressor harness wires. Actual
measurements may be a little different, but should be approximately:
Orange – Red: 1.1Ω, Orange – Brown: 1.9Ω, Red – Brown: 2.7Ω. If the
Orange-Red and Orange-Brown measurements are open (infinite) but the
Red-Brown measurement is normal, than the compressor overload switch
under the compressor cap needs to be replaced. If just one is open, then it
is likely a connection at the compressor has come loose – remove the
compressor cap and check the terminal connections.
If the voltage is 0 VAC, inspect the large disk-like component (this is a varistor
and it is usually blue or black in color) on the power board right next to the
compressor terminals. If this component looks scorched or cracked, replace the
power board. If the varistor does not look damaged then the problem is with
the control board and it must be replaced.
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