Pressure Transducers; Defrost Air Switch; Figure 8−30 Typical Setup For Testing High Pressure Switch - Carrier VECTOR 6500 Operation & Service Manual

3. If the suction pressure does not change, this is an in-
dication the valve is stuck and the piston and drive
motor assembly is to be replaced.
d. Replacing Expansion Valve & Screen
1. Pump down the low side. (Refer to section 8.6.2).
2. Remove coil and unbraze valve. Clean all tube stubs
so new valve fits on easily.
3. Use a wet rag to keep the replacement valve cool and
braze in place.
4. Leak check and evacuate the low side. Refer to Sec-
tions 8.6.3 and 8.6.4.
8.8.7 High Pressure Switch
a. Replacing High Pressure Switch
1. Pump down the compressor (Refer to section 8.6.2).
2. Disconnect wiring from switch, and remove switch.
3. Install switch after verifying switch settings. (Refer to
following step b.)
4. Leak check and evacuate the compressor. Refer to
Sections 8.6.3 and 8.6.4.
b. Checking High Pressure Switch
WARNING
Do not use a nitrogen cylinder without a
pressure regulator. Cylinder pressure is
approximately 2350 PSIG (160 bar). Do not
use oxygen in or near a refrigerant system
as an explosion
Figure 8−30.)
1
2
3
1. Cylinder Valve and Gauge
2. Pressure Regulator
3. Nitrogen Cylinder
4. Pressure Gauge 0 to 400 PSIG
(0 to 27.2 bar)
5. Bleed-Off Valve
6. Switch
Figure 8−30 Typical Setup for Testing High
Pressure Switch
may occur. (See
4
5
6
1. Remove switch as outlined in preceding section
2. Connect ohmmeter or continuity light across switch
terminals. Ohmmeter will indicate resistance and
continuity light will be illuminated if switch closed after
relieving pressure.
3. Connect switch to a cylinder of dry nitrogen. (See
Figure 8−30)
4. Set nitrogen pressure regulator higher than open set-
ting for switch being tested. For pressure switch set-
tings refer to Section 2.10.
5. Close valve on cylinder and open bleed-off valve.
6. Open cylinder valve. Slowly close bleed-off valve and
increase pressure until the switch opens. If light is
used, light will go out and if an ohmmeter is used, the
meter will indicate open. Close cylinder valve. Slowly
open bleed-off valve (to decrease pressure) until
switch closes (light will illuminate or ohmmeter will in-
dicate open).

8.8.8 Pressure Transducers

The Compressor Discharge Pressure Transducer
(CDP) has a range of 0 to 500 PSIG (0 to 34.0 bar) while
the Compressor Suction Pressure Transducer (CSP)
and Evaporator Pressure Transducer (EVOP) have a
range of -14.7 to100 PSIG (-1 to 6.8 bar). To test the
transducers, do the following:
The Compressor Discharge Pressure on the
microprocessor Data List will never read less
than 0 bar/psig, even if it is exposed to a
vacuum (such as when evacuating the system.)
Also, the compressor suction pressure and
evaporator pressure transducers will never
read higher than 100 psig, even if the actual
pressure is higher.
a. Verify that the wiring to the transducer is correct.
b. Power up the transducer circuit. Place the unit in PC
mode, refer to Section 5.3. Check Voltage to trans-
ducer connector. Voltage reading between B (posi-
tive) and A (negative) should be 5.0 VDC.
c. To check the signal wiring, check continuity between
the transducer connector C terminal and the following
microprocessor connector:
CDP = 1MP05, CSP = 1MP29, EVOP = 1MP06
d. If voltage and signal wire are good, replace the trans-
ducer. The transducer may be removed by discon-
necting the connector and quickly backing it off the
Schrader valve fitting.

8.8.9 Defrost Air Switch

If the DTT temperature is above 40°F (4.4°C)
defrost cannot be initiated and the Message-
Center will display "CANNOT START DEFROST
CYCLE".
a. Check air switch tubing. Red tube is to be connected to
the high connection and routed below the coil. Clear
8−31
NOTE
NOTE
62-11389