Carrier 48NHT024 - Page 22

occurred, check each electrical component with the proper
electrical instrumentation. Refer to the unit wiring label
when making these checkouts.
NOTE: Refer to the heating and/or cooling sequence of oper¬
ation in this publication as an aid in determining proper con¬
trol operation.
I. Refrigerant Circuit
Inspect all refrigerant tubing connections and the unit base
for oil accumulations annually. Detecting oil generally indi¬
cates a refrigerant leak.
If oil is detected or if low cooling performance is suspected,
leak-test all refrigerant tubing; using an electronic leak-
detector, halide torch, or liquid-soap solution. If a refriger¬
ant leak is detected, see Step 7, part B, “Refrigerant
Leaks,” in this publication.
If no refrigerant leaks are found and low cooling perform¬
ance is suspected, see Step 9, part B, “Checking and
Adjusting Refrigerant Charge,” in this publication.
J. Gas Input
The gas input does not require checking unless improper
heating performance is suspected. If a problem exists, refer
to Step 8 of this publication.
K. Evaporator Airflow
The heating and/or cooling airflow does not require checking
unless improper performance is suspected. If a problem
exists , be sure that all supply- and return-air grilles are open
and free from obstructions, and that the air filter is clean .
When necessary, refer to Step 9, part C, of this publication
to check the system airflow.
L. Metering Device Servicing
See Fig. 15 for metering device components. The piston has
a refrigerant metering orifice through it. The retainer forms
a sealing surface for liquid line flare connection. To check,
clean or replace piston:
1. Shut off power to unit.
2. Remove refrigerant from unit using approved refriger¬
ant removal methods.
3. Remove liquid line flare connections from metering
device.
4. Note position of arrow on metering device body with
respect to unit.
5. Pull retainer out of body. Be careful not to scratch flare
sealing surface. If retainer does not pull out easily,
carefully use locking pliers to remove retainer. Replace
scratched or damaged retainer.
6. Slide piston out by inserting a small soft wire through
metering hole (18-gage thermostat wire). See that
metering hole, sealing surface around piston cones and
fluted portion of piston are not damaged.
7. Chart on unit access panel illustrates proper arrange¬
ment and size of piston. See Table 17 for piston sizes.
8. Clean piston refrigerant metering orifice.
9. Replace retainer O-ring Part No. is 99CC501052.
M. Liquid Line Strainer
The Liquid Line Strainer (to protect metering device), is
made of wire mesh and located in the liquid line on inlet
side. Strainer is pressed into the fine. Remove strainer by
threading a No. 10 sheet metal screw into strainer and pull¬
ing the screw with pliers.