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AIR CONDITIONING
24-1 7
watch both suction gauges for the following reac-
tions.
(1) Pressure registered at the evaporator suction
gauges will become progressively lower.
(2)
At the same time the compressor inlet gauge
will start to fluctuate. This fluctuation is caused by
the alternately opening and closing of the "EPR'
valve. It indicates that suction pressure is reduced to
the point where
it
just about balances the internal
gas pressure in the bellows. The "EPR' valve
is
ac-
tually operating as a modulating valve.
(3) When fluctuation at the compressor inIet gauge
stops and the pressure registered drops steadily, the
"EPR" valve is maintaining minimum suction line
pressure. Allow pressure registered at the compres-
sor inlet gauge to drop 15 psi or lower, then read the
evaporator suction gauge.
NOTE: If, and only if the compressor inlet pressure
will not pull down to
15
psi, increase engine speed
to approximately
2000
rpm.
(4)
The suction gauge pressure should be
22
to
26
psi. This indicates that the suction pressure main-
tained by the "EPR" valve
is
correct. Again, deter-
mine the pressure at which the valve is fully open.
(5)
Turn the blower switch to position NO.
2
and
push in the "Cool" button to increase the heat load
on the evaporator. This will increase suction pres-
sure, causing the "EPR" valve to open fully.
(6)
Watch both the evaporator suction and the
compression inlet pressure gauge. The pressure reg-
istered at the compressor inlet gauge will increase
quite rapidly. Both suction gauges should again stabi-
lize at a pressure of
26
psi or slightly higher within a
few minutes.
If the minimum suction pressure registered step
(4)
above is
22
to
26
psi and the suction pressure reg-
istered with the valve fully open step
(6)
above is
26
psi or slightly higher, the "EPR' valve is function-
ing normally. A system which passes both the Over-
All Performance Test and the "EPR" Valve Test re-
quires no further tests.
Suction Pressure Above
26
psi. If the
minimum
SUC-
tion pressure is higher than
26
psi step
(4)
above, the
evaporator will not get
as
cold as it should for maxi-
mum performance. It will be necessary to replace the
"EPR" valve. Repeat the "EPR" valve test and the
Performance Test.
Suction Pressure Below
22
psi. If
suction pressure
goes below
22
psi step
(4)
above, the evaporator is
too cold. The correction is to replace "EPR" valve
and repeat the "EPR' valve test.
If the system failed to pass the Over-All Perform-
ance Test but passed the "EPR' valve test, proceed
with the Compressor Capacity Test
7.
PART 2
This part of the test will save time as the expansion
valve and compressor are being tested during the
EPR valve test. There is always a definite relationship
between the temperature and pressure of refrigerant
vapor in a system that's working right; however, this
temperature-pressure relationship will be upset if the
compressor capacity is not up to specifications, or if
the expansion valve is not doing its job properly.
NOTE: If the expansion valve opens too much, the
evaporator will be flooded and there will be liquid
refrigerant leaving the evaporator outlet. If there
is liquid refrigerant along with the vapor, the vapor
can't become superheated and the gas temperature
will be low in relation to pressure.
NOTE:
If
the expansion valve doesn't open enough,
the evaporator will be starved and the liquid re-
frigerant will be vaporized before it gets to the out-
let. As the temperature of the vapor is somewhere
around
30
degrees, it will be cooler than the out-
side air so that the vapor will still absorb some heat
before it leaves the evaporator. This will create a
over-superheated condition where the temperature
will be very high in relation to pressure.
If the compressor capacity is low, it is because the
refrigerant vapor is leaking internally, usually past
the reed valves or a blown gasket. This will be indi-
cated by low discharge pressure. With the refrigerant
being recirculated in the compressor due to the in-
ternal leakage, heat will be generated and the refrig-
erant will absorb some of this heat; superheating the
refrigerant. This will result in a discharge tempera-
ture which will be above the maximum.
When you hook up the gauges, install the thermom-
eter clip on the discharge line, getting the clip as
close to the compressor as possible and making sure
you have a tight contact between the clip and the dis-
charge line. The thermometer bulb must fit tightly in
the loop and none of the bulb should overhang the
clip otherwise you will measure air temperature in-
stead of refrigerant temperature.
NOTE: It i s recommended to wrap the bulb and
clip to insulate them from the engine compartment
heat.
COMPRESSOR DISCHARGE
TEMPERATURE-PRESSURE CHART
DISCHARGE PRESSURE TEMPERATURE
O
FAHRENHEIT
GAUGE READING
(PSI1
MINIMUM
MAXIMUM
190-195
195-200
200-205
205-2
10
21 0-21
5
2 1 5-220
220-225
225-230
168
170
172
174
176
178
180
182
214
21 6
21 8
220
222
224
226
228
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