Maytag Amana PMH Series Service And Troubleshooting page 31

SERVICING
ple gauge. See that the vacuum pump will bank-off to a
minimum of 50 microns. A high vacuum pump can only
produce a good vacuum if its oil is not contaminated.
5. If the vacuum pump is working properly, close the valve
to the vacuum thermocouple gauge and open the high
and low side valves or the high vacuum manifold set.
With the valve on the charging cylinder closed, open the
manifold valve to the cylinder.
6. Evacuate the system to at least 29 inches gauge before
opening valve to thermocouple vacuum gauge.
7. Continue to evacuate to a minimum of 250 microns.
Close valve pump and watch rate of rise. If vacuum
does not rise above 1500 microns in three minutes,
system can be considered properly evacuated.
8. If thermocouple vacuum gauge continues to rise and
levels off at about 5000 microns, moisture and non-con-
densables are still present. If gauge continues to rise a
leak is present. Repair and re-evacuate.
9. Close valve to thermocouple vacuum gauge and vacu-
um pump. Shut off pump and prepare to charge.
Charging
Charge the system with the exact amount of refrigerant.
Refer to the unit nameplate for the correct refrigerant
charge. An inaccurately charged system will cause future
problems.
1. When using an ambient compensated calibrated
charging cylinder, allow liquid refrigerant only to enter
the high side.
2. After the system will take all it will take, close the valve
on the high side of the manifold.
3. Start the system and charge the balance of the refriger-
ant though the low side. Do not charge in a liquid form.
4. Close the low side valve on the manifold and pinch-off
both process tubes. Remove the manifold set, crimp
shut the open ends of the process tubes and braze.
5. Recheck for refrigerant leaks.
NOTE: Do not use a refrigerant other than that shown on
the serial number identification plate.
All precautionary measures recommended by the refriger-
ant manufacturers and suppliers should be observed.
Line Piercing Valves
Line piercing valves may be used for diagnosis but are not
suitable for evacuating or charging due to the minute holes
pierced in the tubing.
Line piercing valves must not be left on the refrigerant sys-
tem. The connection between the valve and the refrigerant
tubing is not hermetically sealed and will eventually leak.
Open Lines
During any processing of the refrigeration system the lines
should never be left open to atmosphere since water vapor
will enter and add to the problem of proper evacuation.
Operating Test
The final step in a successful repair is an accurate operat-
ing test. Follow the Cooling and Heating Performance tests
provided to make sure the product is again performing to
design standards.
Efficient operation is dependent on a balanced system.
One of the most common reasons for inefficiency is the
users failure to adequately clean the condenser thereby
creating reduced air movement.
Cooling Performance Test Thermometers
The following precautions are necessary in observing the
thermometer readings in the cooling performance test.
1. Use two accurately calibrated refrigeration type ther-
mometers or a thermocouple potentiometer.
2. Thermometers are affected by body heat or changes in
air flow. Therefore, the thermometers must be secured
in proper locations with masking tape, wire or other
applicable retainers.
3. Readings should be observed without touching or mov-
ing the thermometers.
Place inlet air
thermostat here
(Center in grille)
Sling Psychrometer
The sling psychrometer is used to obtain the wet bulb tem-
perature in determining the percent relative humidity.
To obtain the wet bulb operate the sling psychrometer as
follows:
Saturate the wick (only once during procedure of obtaining
wet bulb readings) with clean water slightly below room
temperature. Psychrometer reading should be acquired five
to six feet in front of the unit and approximately four feet off
the floor.
NOTE: Direct discharge airflow away from the sling psy-
chrometer.
The cooling performance test should not be employed
when outside temperatures are 20° below that of the room.
Best results are obtained when the test is conducted under
peak load conditions.
The air conditioner must operate at least 20 minutes on the
High Cool position before testing.
Cooling Test
The following temperature must be recorded for the cooling
performance test:
A. Dry bulb temperature of return air at conditioner. Locate
thermometer as illustrated.
Place discharge air
thermostat here
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