Service manual

17
The customer turns the system to fan/low or fan/high and
nothing happens. When he turns the selector switch to
“Cool”, the compressor starts but still no fan.
Question: “What could cause the fan to be dead?”
Answer:
1. “The selector switch could be open.”
The safest way to check a selector switch is to turn
off all power, remove the wires and with an ohm
meter, check for continuity between terminals L&1
for low speed fan connection and terminals L&2 for
high speed fan connection. The meter should read 0
ohms.
Terminals Switch Position
L-1-3 Lo Heat
L-1 Lo Fan
L-2 Hi Fan
L-1-4 Lo Cool
L-2-4 Hi Cool
2. “Fan motor windings could be open, shorted or
grounded.”
Be sure power is off. Check motor windings per
instructions (See page 8).
3. The electrical circuit to the fan motor leads could be
open. Check all connections (including wire nuts) to
the fan motor red, black and white wires.
4. “Fan capacitor may be shorted, weak or open.”
To check fan capacitor, follow same procedure that
is outlined for compressor run capacitors (See page
9).
Problem
9. Compressor runs but won’t pump.
The customer turns the selector to a “Cool” position and the
thermostat to a low temperature setting (below room
temperature). The fan runs OK, but the unit does not cool.
On examination we find that the compressor does run. It
runs quietly and smoothly. We check the compressor current
and find that it is below the FLA rating. The evaporator is
warm, the suction line is warm. There are two possible
problems, either the compressor valves are broken or the unit
is completely out of charge. At this point, you must break
into the system to locate the problem.
Problem
10. Compressor cycling off and on.
The customer says he gets inadequate cooling even though he
has several times set the thermostat down to call for a lower
temperature until it is now all the way down to the lowest
possible setting.
On investigation, we find that the compressor is cycling off
and on.
Question: “What could cause the compressor to cycle
off and on?”
Answer: “Two things.”
1. “The thermostat is out of calibration. Turn off power.
Check with ohm meter.”
2. “The compressor is cycling on the thermal current
overload.”
With the power on, check the voltage between the
terminals of the overload while the compressor is not
running. If the meter reads 115 volts domestic USA
models or 240 volts export/overseas models, the
compressor is cycling on this switch (see page 8 for
description and function of this switch).
Question: “What could cause the switch to open and
close?”
Answer: “Compressor is running hot or compressor is
drawing excess current or both.”
Check by:
1. Feeling the compressor dome - it will normally
(during warm weather - above 85°) be too hot to be
comfortable if you keep your hand on it. If it is
burning hot, it is probably overheating. The normal
compressor housing temperature varies with outside
temperature and evaporator load so determining
whether or not it is too high is a matter of judgement
based on experience.
2. Measuring the current (amperes) through the black
wire which leads from #5 on the potential relay to the
overload switch. This current may be compared to
the unit FLA rating.
Remember that the overload switch is sensitive to both high
temperature and high current. Since this is true, we can’t
specify a definite temperature or amperage at which the
switch will open. As the temperature rises, the current at
which the switch will open goes down. As the temperature
goes down, the current at which the switch will open goes
up.