Table of Contents
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1
2
3
1. Cylinder Valve and
Gauge
2. Pressure Regulator
3. Nitrogen Cylinder
4. Pressure Gauge
(0 to 500 psig =
0 to 36 kg/cm@)
Figure 4-6. Checking High Pressure Switch
WARNING
Do not use a nitrogen cylinder without a
pressure regulator. Cylinder pressure is
approximately 2350 psi (165 kg/cm@). Do not
use oxygen in or near a refrigeration system
as an explosion may occur.
d. Back-off regulator adjustment completely.
Open the cylinder valve.
e. Slowly open the regulator valve to increase the
pressure to the applicable pressures listed in
Table 4-1 open or close the switch. If the
ohmmeter reading does not correspond with
the pressure listed in Table 4-1, the switch is
defective and should be replaced.
f.
Close cylinder valve and release the pressure
through the bleed-off valve. As the pressure
drops, the applicable switch will open or close.
If the ohmmeter reading does not correspond
with the pressure listed in Table 4-1, the switch
is defective and should be replaced.
T-288
4
5
8
6 7
5. Bleed-Off Valve
6. 1/4 inch Connection
7. High or Low Pressure
Switch
8. Ohmmeter
Table 4-1. Pressure Switch Continuity Check
R-134a
R-134a
No Continuity
Switches
(Switch Opens )
High Press-
300 10 psig
ure (HPS)
Low Press-
6 3 psig
ure (LPS)
Condenser
250 10 psig
Fan Speed
(CFS)
Unloader
35 2 psig
Pressure #1
(UPS1)
Unloader
31 2 psig
Pressure #2
(UPS2)
Unloader
220 15 psig
Pressure #3
(UPS3)
4.12 THERMOSTATIC EXPANSION VALVE
The thermostatic expansion valve is an automatic
device which maintains constant superheat of the
refrigerant gas leaving the evaporator regardless
of suction pressure. The valve functions are: (a)
automatic response of refrigerant flow to match
the evaporator load and (b) prevention of liquid
refrigerant entering the compressor. Unless the
valve is defective, it seldom requires any
maintenance.
a. Replacing the Expansion Valve
1. Pump down the unit. (Refer to section 4.4)
2. Remove return air access panel.
3. Loosen flare nut and disconnect equalizer line
from expansion valve.
4. Remove roadside evaporator motor access
panel.
5. Remove insulation (Presstite) from expansion
valve bulb located on suctionline entering
liquid-suction heat exchanger (LSHX).
6. Loosen bulb securing strap and pull bulb
through to bus interior.
7. Remove flange screws and lift off power head
and cage assemblies. Check for foreign
matieral in valve body.
8. Install new gaskets and assemble new cage
and power head assemblies.
4-8
Ohmmeter Reading
Continuity
(Switch Closes)
200 10 psig
25 3 psig
190 15 psig
26 2 psig
23 2 psig
270 15 psig
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