Page 14
essary for checking the charge. Block equal sections of air
intake panels and move obstructions sideways until the liq-
uid pressure is in the 200−250 psig (1379−1724 kPa) range.
See figure 15.
Blocking Outdoor Coil
cardboard or
plastic sheet
Outdoor coil should be
blocked one side
at a time with cardboard
or plastic sheet until proper
testing pressures
are reached.
Figure 15
1 − With the manifold gauge hose still on the liquid service
port and the unit operating stably, use a digital ther-
mometer to record the liquid line temperature.
2 − At the same time, record the liquid line pressure reading.
3 − Use a temperature/pressure chart for HCFC-22 to de-
termine the saturation temperature for the liquid line
pressure reading.
4 − Subtract the liquid line temperature from the saturation
temperature (according to the chart) to determine sub-
cooling.
(Saturation temperature − Liquid line tem-
perature = Subcooling)
5 − Compare the subcooling value with those in table 4. If
subcooling is greater than shown, recover some refrig-
erant. If subcooling is less than shown, add some re-
frigerant.
Table 4
Subcooling Values
Model
Subcooling
_
F (
_
C)
HP27−024
8 + 2 (4.4 + 1)
HP27−030
7 + 2 (3.9 + 1)
HP27−036
8 + 2 (4.4 + 1)
HP27−042
7 + 2 (3.9 + 1)
Charging Using Normal Operating Pressures
and the Approach Method
Outdoor Temp. > 65
F (18
C)
The following procedure is intended as a general guide and
is for use on expansion valve systems only. For best results,
indoor temperature should be 70°F (21°C) to 80°F (26°C).
Monitor system pressures while charging.
1 − Record outdoor ambient temperature using a digital
thermometer.
2 − Attach high pressure gauge set and operate unit for
several minutes to allow system pressures to stabilize.
3 − Compare stabilized pressures with those provided in
table 6, Normal Operating Pressures." Minor varia-
tions in these pressures may be expected due to differ-
ences in installations. Significant differences could
mean that the system is not properly charged or that a
problem exists with some component in the system.
Pressures higher than those listed indicate that the
system is overcharged. Pressures lower than those
listed indicate that the system is undercharged. Verify
adjusted charge using the approach method.
Approach Method
4 − Use the same digital thermometer used to check out-
door ambient temperature to check liquid line tempera-
ture. Verify the unit charge using the approach method.
5 − The difference between the ambient and liquid temper-
atures should match values given in table 5. If the val-
ues don’t agree with the those in table 5, add refriger-
ant to lower the approach temperature or recover
refrigerant from the system to increase the approach
temperature.
Table 5
Approach Values
Model
Liquid Temp. Minus Ambient
Temp.
_
F (
_
C)
HP27−024
8 + 1 (4.4 + .5)
HP27−030
5 + 1 (2.8 + .5)
HP27−036
5 + 1 (2.8 + .5)
HP27−042
8 + 1 (4.4 + .5)
IMPORTANT
Use table 6 as a general guide when performing
maintenance checks. This is not a procedure for
charging the unit (Refer to Charging/Checking
Charge section). Minor variations in these pressures
may be expected due to differences in installations.
Significant differences could mean that the system
is not properly charged or that a problem exists with
some component in the system.
