Electrical System Component Service; Megohmmeter Test Procedure; Figure 8−31 Defrost Air Switch Test Setup - Carrier VECTOR 6500 Operation & Service Manual

tube is to be connected to the low connection and
routed above coil. Check condition and mounting of air
sensing fittings on the coil end of both tubes.
b. To check the defrost air switch, run unit in cooling and
jumper across the air switch terminals. This will start
the defrost cycle as it simulates the action of the de-
frost air switch. Bypassing the switch in this manner
operates all components involved in defrost.
c. Unit should remain in defrost until the DTT reaches
55_F (12.8_C ), for normal defrost, or after 5 to 10
minutes, for natural defrost (refer to Section 4.6 for
more information on defrost). At this point the defrost
cycle will terminate, and the unit will resume auto-
matic operation.
d. If the above test indicates satisfactory operation, test
DAS settings using a Magnehelic gauge (Carrier
Transicold part number 07-00177) or similar instru-
ment as follows.
2
5
6
1. Ohmmeter or Continuity Device
2. Adjustment Screw
(0.050" socket head size)
3. Low Side Connection
4. Pressure Line or Aspirator Bulb (Carrier
Transicold part number 07-00177-01)
5. Magnehelic Gauge (Carrier Transicold part
number 07-00177-00)
6. High Side Connection
Figure 8−31 Defrost Air Switch Test Setup
e. Ensure magnehelic gauge is in proper calibration.
NOTE
The magnehelic gauge may be used in any
position, but must be re-zeroed if position of
gauge is changed from vertical to horizontal or
vice versa. USE ONLY IN POSITION FOR
WHICH IT IS ZEROED.
f. With air switch in vertical position, connect high pres-
sure side of magnehelic gauge, a tee and and aspir-
ator to high side connection of air switch. Tee is to be
placed approximately half-way between gauge and air
switch or an improper reading may result. (See
Figure 8−31)
62-11389
3
4
1
g. Attach an ohmmeter to the air switch electrical con-
tacts to check switch action.
Use a hand aspirator (Carrier Transicold part
number 07-00177-01), since blowing into tube
by mouth may cause an incorrect reading.
h. With the gauge reading at zero, apply air pressure
very slowly to the air switch. An ohmmeter will indi-
cate continuity when switch actuates. The switch
contacts should close and the ohmmeter needle
move rapidly to 0. Any hesitation in the ohmmeter in-
dicates a possible problem with the switch, and it
should be replaced.
i. Refer to Section 2.10 for switch setting. If switch fails to
actuate at correct gauge reading, adjust switch by turn-
ing adjusting screw clockwise to increase setting or
counterclockwise to decrease setting.
j. Repeat checkout procedure until switch actuates at
correct gauge reading.
k. After switch is adjusted, place a small amount of
paint or fingernail polish on the adjusting screw so
that vibration will not change switch setting.
8.9 ELECTRICAL SYSTEM COMPONENT
SERVICE
Procedures for servicing or maintaining the high voltage
electrical system components are provided in the
following sub-paragraphs.

8.9.1 Megohmmeter Test Procedure

This instruction will aid in the check of the electrical
wiring insulation
connections.
A megohmmeter test instrument (commonly known as a
Megger) can be purchased locally at most electrical
supply centers. This test requires a meter that can be
set to 1000V.
Before connecting a megohmmeter, place
the Main Power switch in the OFF position.
Disconnect the high voltage source, lock-
out/tagout the receptacle and disconnect
the negative battery connection. Isolate the
microprocessor by disconnecting all con-
nectors and wires going to it. Observe Na-
tional Electric Manufacturer's Association
(NEMA) rules and test equipment manufac-
turers instructions.
a. Disconnect the generator ground wire (GEN-GRD =
green wire marked with red tape) from the unit ground
plate (PE plate) inside the control box. See
Figure 8−32.
b. Connect a megohmmeter lead to the ground plate.
8−32
NOTE
integrity and field
CAUTION
electrical