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Diagnostic Information
Low Side leaks
Low side leaks consist of a break in the system at the
evaporator, low side (suction) return line, or accumulator.
If a leak is found in any of these areas, moisture has
probably entered the system. The compressor and drier
will have to be replaced and the system will need to be
flushed thoroughly with nitrogen gas and evacuated to
50 microns before re-charging.
High Side Leaks
High side leaks consist of a break in the system at the
condenser, high side tubing, drier, or capillary tube. If a
leak is found in any of these areas, the system can be
flushed with nitrogen gas, evacuated to 50 microns, and
re-charged.
Restricted Capillary Tube
Moisture or other contaminants that enter the system
can cause deposits in the system. These deposits will
usually collect in the capillary tube and form a restriction
that cannot be completely removed by flushing. If the
capillary tube is found to be restricted, the evaporator,
compressor, condenser, and drier should all be replaced.
Access Valves
A temporary access valve can be used to service or
evaluate the system. From these access valves, you
can evacuate, charge, and recover the system. The
access valve can be installed on the compressor's
process tube (this will also be a low pressure side). Be
sure to cap off access valve while servicing. This will
prevent contamination of the system and/or refrigerant
from leaking. After servicing, the access valve should
be removed. A pinch-off tool can be used to close the
system to remove the access valve and then braze the
hole for the access valve to seal the system. Be sure to
leak check after brazing.
Evaporator Frost Pattern
Checking the evaporator frost pattern is a good way
to quickly diagnose simple sealed system problems.
This can be done by allowing the unit to run (at least 10
minutes) with the door open for at least 5 minutes. This
will help speed up the normal frosting of the evaporator
plate. By visually inspecting the evaporator and feeling
it with your hands, you will see and feel frost across the
plate. It is absolutely necessary for the frost to cover the
entire evaporator plate. This will ensure the system has
been charged to its specified amount or does not have
a leak. A partial frost pattern may lead to excessive run
times or even 100% run mode. This is because the frost
does not reach the area of the evaporator thermistor, so
it does not sense the temperature required to cycle the
unit off.
6
Pressure and Temperature
There are two ways to measure temperature of the
evaporator plate:
1.
Use a thermocouple to measure the temperature of
evaporator plate. Thermocouple must be secured to
the evaporator when taking the measurement.
2.
If there is proper contact between the thermistor and
evaporator plate, thermistor resistance value can be
corresponded to the temperature (See Thermistors).
NOTE: Temperature and pressure readings must
be taken while unit is running. Use gauge
pressure readings from the compressor's
process tube (low side) access valve.
Pressure will vary depending upon the ambient
temperature and current stage of operation for the unit.
For example, the unit will have pressure between 0 and
5 psi just before entering the off cycle. Normal running
pressures on the low side will average 5 to 10 lbs.
Temperature-Pressure Chart for R-134a
Degrees F
Pressure (psi)
-12
-8
-4
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
If low side pressure is below pressure in chart above,
check for the following:
1.
A system leak
2.
Capillary tube is restricted
3.
Insufficient compressor (does not pump properly)
If low side pressure is above pressure in chart above,
check for the following:
1.
Restricted air flow
2.
Dirty condenser coil
3.
Overcharged system
4.
Low side leak
SMR-0003
Degrees F
R-134a
1.1
36
2.8
38
4.5
40
6.5
42
7.5
44
8.5
46
9.6
48
10.8
50
12.0
52
13.1
56
14.4
60
15.7
64
17.0
68
18.4
72
19.9
76
21.4
80
22.9
84
24.5
88
26.1
92
27.8
96
29.5
100
© Viking Range Corporation
Pressure (psi)
R-134a
31.3
33.2
35.1
37.0
39.1
41.1
43.3
45.5
47.7
52.3
57.5
62.7
68.3
74.2
80.3
86.8
93.6
100.7
108.2
116.1
124.3
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