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pressure port. The difference in these two pressures will be the pressure drop across the filter, check valve, and
solenoid valve. The pressure drop across the check valve and solenoid valve is approximately 0.4 bar, which should
be subtracted from the two oil pressure measurements to give the oil filter pressure drop.
10.8.3 - Compressor rotation control
Correct compressor rotation is one of the most critical application considerations. Reverse rotation, even for a very
short duration, damages the compressor.
The reverse rotation protection scheme must be able to determine the direction of rotation and stop the compressor
within 300 ms. Reverse rotation is most likely to occur whenever the wiring to the compressor terminals is disturbed.
To minimize the opportunity for reverse rotation, the following procedure must be applied. Rewire the power cables
to the compressor terminal pin as originally wired. For replacement of the compressor, a low pressure switch is
included with the compressor. This low pressure switch should be temporarily installed as a hard safety on the high
pressure part of the compressor. The purpose of this switch is to protect the compressor against any wiring errors at
the compressor terminal pin. The electrical contact of the switch would be wired in series with the high pressure
switch. The switch will remain in place until the compressor has been started and direction of rotation has been
verified; at this point, the switch will be removed. The switch that has been selected for detecting reverse rotation is
Carrier part number HK01CB001. This switch opens the contacts when the pressure falls below 7 kPa. The switch is
a manual reset type that can be reset after the pressure has once again risen above 70 kPa. It is critical that the
switch be a manual reset type to preclude the compressor from short cycling in the reverse direction.
10.9 - Precaution for compressor power supply bus bar connection
This note applies to units using power supply bus bars with riveted contact block at the level of the connection cages
in the control box. During re-connection it is imperative to:
• engage each bus bar in the cage up to the stop
• ensure visually that the bus bars have good contact at the connection areas: there must not be any free
movement between the bus bar and the connection area created by the fixing rivet of the contact block.
Connection of the contactor or current transformer
Carrier Yileng - Shanghai, China
45
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