Carrier TRANSICOLD Vector 8500 Operation & Service Manual Download

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8.8.11

Defrost Air Switch

Figure 8.28 Defrost Air Switch Test Setup

1. Ohmmeter or Continuity Device
2. Adjustment Screw (0.050” socket head size)
3. Low Side Connection
4. Pressure Line or Aspirator Bulb (Carrier Transi-

cold part number 07-00177-01)

5. Magnehelic Gauge (Carrier Transicold part

number 07-00177-00)

6. High Side Connection

- - - - -

NOTE

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”.

1. Check air switch tubing. Red tube is to be con-

nected to the high connection and routed below
the coil. Clear tube is to be connected to the low
connection and routed above coil. Check condi-
tion and mounting of air sensing fittings on the
coil end of both tubes. See

Figure 2.3

2. To check the defrost air switch, run unit in cool-

ing and jumper across the air switch terminals.
This will start the defrost cycle as it simulates
the action of the defrost air switch. Bypassing
the switch in this manner operates all compo-
nents involved in defrost.

3. Unit should remain in defrost until the DTT and

SAT both reach 55°F (12.8°C). At this point the
defrost cycle will terminate, and the unit will
resume automatic operation.

4. If the above test indicates satisfactory operation,

test DAS settings using a Magnehelic gauge
(Carrier Transicold part number 07-00177) or
similar instrument as follows.

5. Ensure magnehelic gauge is in proper calibra-

tion.

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.

6. With air switch in vertical position, connect high

pressure side of magnehelic gauge, a tee and
and aspirator 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 8.28

)

7. Attach an ohmmeter to the air switch electrical

contacts to check switch action.

NOTE

Use a hand aspirator (Carrier Transicold part
number 07-00177-01), since blowing into tube
by mouth may cause an incorrect reading.

8. With the gauge reading at zero, apply air pres-

sure very slowly to the air switch. An ohmmeter
will indicate continuity when switch actuates.
The switch contacts should close and the ohm-
meter needle move rapidly to 0. Any hesitation
in the ohmmeter indicates a possible problem
with the switch, and it should be replaced.

9. Refer to

Section 2.9

for switch setting. If switch

fails to actuate at correct gauge reading, adjust
switch by turning adjusting screw clockwise to
increase setting or counterclockwise to
decrease setting.

10. Repeat checkout procedure until switch actu-

ates at correct gauge reading.

11. 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.