Carrier VECTOR 1800 MT, Руководство по эксплуатации и обслуживанию

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8-28 62-11039
8.17.2 EVXV coil (Unipolar design)
A
B
B
A
ORN RED
YEL GRY BLK
COM (+12VDC)
Figure 8--30 Electronic expansion valve
The EVXV (evaporator expansion valve) coil consists of
four windings. See Figure 8--30 for labelling.
All of the windings are connected together at one end,
sharing a common wire where +12V is applied from the
micro.
The other end of each winding has its own wire
connected back to the micro.
Looking at the 5--pin connector on the EVXV coil, the
wiring is as follows:
Connector Pin Wire Color Winding
A ORANGE A
B RED B
C YELLOW
A
D BLACK
B
E GREY COM (+12V)
Each winding has a resistance of about 46 ohms. If the
coil is good, this resistance (
¦
10 %) will be measured
between the gray common wire and each of the other
four wires.
Also, since the coils are all connected together at a
common point, the resistance of two windings in series
can be measured between any two wires other than the
gray wire. This resistance will be about 92 ohms
(
¦
10%).
To open the valve, the micro energizes each winding of
the coil in a specific sequence. Energizing the windings
in the correct sequence rotates the rotor and causes the
valve to open one step.
The windings are energized in the reverse sequence to
close the valve one step.
If the windings are not energized in the proper
sequence, the valve will chatter, but the rotor will not
rotate and the valve will not open (or close).
The sequence to energize each coil is shown below:
O
P
A
P
E
A & B
E
N
B
A & B
A
C
L
A & B
L
O
B
O
S
E
A & B
E
D
+12 VDC on GRAY
8.18 THERMOSTATIC EXPANSION VALVES
(REMOTE COMPARTMENTS)
NOTE
Place unit in Service Mode before performing
the following operations on the unit. Refer to
Section 5.2.3
The thermostatic expansion valve (TXV) 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.
8.18.1 Replacing Expansion Valve & Screen
a. Pump down the unit by closing the manual shut off
valve (king valve). (Refer to Section 8.10.1.)
b. Remove insulation (Presstite) from expansion valve
bulb and then remove bulb from suction line.
c. Remove Presstite from the expansion valve power
head. Unscrew power head if only the element is be-
ing changed and replace by reversing steps a.
through c.
d. Use a wet rag to keep valve cool whenever brazing.
Heat inlet, outlet and equalizer connection to valve
body and remove valve. Clean all tube stubs so new
valve fits on easily.
e. Install new valve and screen, with cone of screen
pointing into liquid line at inlet to the valve by revers-
ing steps a.through c.
f. The thermal bulb is located below the center of the
suction line (See Figure 8--31). This area must be
clean to ensure positive bulb contact. Firmly tighten
the straps around the thermal bulb and suction line
and insulate both with Presstite.
g. Evacuate by placing vacuum pump on suction ser-
vice valve.
h. Open king valve and then check refrigerant level.
i. Check superheat. (Refer to Section 2.12)
j.Check unit operation by running Pretrip (Refer to Sec-
tion 3.5).