45
SERVICING
Place discharge air
thermostat here
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 ob-
taining wet bulb readings) with clean water slightly be-
low room temperature. Psychrometer reading should be
acquired five to six feet in front of the unit and ap-
proximately four feet off the floor.
NOTE:
Direct discharge airflow away from the sling
psychrometer.
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. Lo-
cate thermometer as illustrated.
B. Dry bulb temperature of air leaving conditioner. Ther-
mometer has to be located as illustrated.
C. The dry bulb thermometer temperature on the sling psy-
chrometer should be plus or minus 1°F within
reading
obtained on thermometer in the return air. Check wet
bulb temperature on sling psychrometer and record
same.
D. After the wet bulb temperature, dry bulb temperature,
and return air temperature have been recorded, pro-
ceed to calculate the temperature difference as follows.
E. Subtract temperature obtained in Step B from tempera-
ture obtained in Step A. The remainder temperature is
used to
calculate from the Cooling Range Chart.
EXAMPLE:
Assume a PTH15 unit is under test and the tem-
perature readings indicated below were obtained.
1. Return air D.B. temperature: 80°F, Step A.
2. Discharge air D.B. temperature: 69°F, Step B.
3. Return air, wet and dry bulb temperature as recorded
in Step C: Dry Bulb 80°F, Wet Bulb 75°F.
4. In left hand column of Cooling Capacity Charge headed
Dry Bulb, find the 80° value.
5. In column headed Wet Bulb find the 75°F value and find
the value 8 -13 in the cooling range column under the
Model "PTH153 PTH154".
This data shows that the temperature of the air passing
through the cooling coil is reduced at least 8°F but not more
than 13°F. This example unit is operating normally for the
existing conditions.
For the example unit under test, the temperature differ-
ence was 11°F (80°F, return air, minimum 69°F discharge
air). Since the value is within the listed cooling range 8 -
13, this unit is considered to be operating normally.
For Total Power Input Test (wattage) the following addi-
tional readings must be recorded after the unit under
test is interconnected with a wattmeter.
• Outdoor dry bulb temperature. Avoid direct exposure
of thermometer to sunlight or to hot condenser dis-
charge air.
• Total watts input, measured by wattmeter or calculate
by multiplying applied voltage by unit amps.
Calculating Procedure
1. Locate the outdoor temperature obtained in first col-
umn of Total Power Consumption Cooling Chart.
2. Locate in second column the return air wet bulb tem-
perature obtained in Step C.
3. The total watts input should come between minimum
and maximum values indicated for each model.
EXAMPLE:
Assume that a PTH15 is again under test. Pro-
ceed as follows and observe test readings as simultaneously
as possible.
1. Outdoor dry bulb temperature reading - 95°F.
2. Check watts input - 1510.
3. Wet bulb temperature as described in Step C - 75°F.
In column headed Outdoor Dry Bulb Temperature of the Power
Consumption Chart find the 95°F value. Read to the right
from the 95°F value and find the room wet bulb tempera-
ture (75°F).
