Service manual

19
6. “Plugged up cap tube.”
A cap tube can become stopped up by oil sludge or
contaminants in the system. This will only occur if
the system has been open to allow moisture or other
contaminants to enter the system or if the
compressor has been overheated for a lengthy period
of time.
It is difficult to determine the difference between a stopped
up cap tube and a low charge because the symptoms will be
nearly the same.
To repair either a low charge or stopped up cap tube,
we will have to install service valves and attach
gauge manifold. If after the correct amount of
refrigerant has been charged into the system, and it
has low charge symptoms, we will know the cap tube
is plugged and will have to be replaced.
Problem
12. No heat - Heat Strip.
The customer says that he has turned the selector switch to
“Heat” position and the blower works OK, but no heat.
Question: “What are the possible causes of “no heat”
problem?”
Answer: 1. “The limit switch or the heating
element could be open.” Check
with continuity.
2. “The selector switch could be open
(See page 7).”
3. “The thermostat could be open
(See page 7).”
In all three cases, turn off power and check
for continuity with an ohm meter.
Problem
13. Cooling Performance Check
Make sure the filters, the evaporator coil and the condenser
coils are clean and all supply air registers are open wide.
1. Start the air conditioning unit and allow it to run for
at least one-half hour. Possibly longer if it is
extremely warm outside (the objective is to saturate
the evaporator coil before we begin running a
temperature test).
2. With a standard dial type or digital thermometer,
measure the temperature of the air immediately
entering the return air grille of the air conditioning
unit.
3. Subtract from this temperature the temperature of the
air immediately leaving the supply air louvers (if it is
a ducted air conditioning unit, use the closest
discharge register and make sure the temperature
sensing device is measuring supply air temperature
only).
4. A properly running air conditioning unit should have
a temperature difference of approximately 18 to 22
degrees F. Note: Slightly less temperature differences
are possible under extremely humid conditions. (The
unit may have to run longer to remove moisture).
5. Temperature differences greater than 22 degrees are
possible in warm dry weather. Restricted air flow
over the evaporator may also cause greater than 22
degree temperature differences.
6. Compressor running amps should be checked as
follows. Note the amperage listed on the air
conditioner rating plate (RLA) is determined at
design conditions only. These conditions are 95
degrees outdoor temperature and 80 degrees indoor
temperature.
Since the outdoor temperature is mostly responsible
for the amount of compressor amperage, this figure
will have to be adjusted for changes in outdoor
temperature approximately 1 amp for every 5 degrees
in temperature change (from 95 degrees) up or down
accordingly.