Exchanger Economizer - Carrier Pro-Dialog CONTROL 4 User Manual

4.7 - Motor Cooling Control with sub cooling plate exchanger
The sub cooling plate exchanger replaces the old economizer for simple maintenance and cost reduction. Thus the
screw compressor motors are cooled by refrigerant from the plate exchanger, located between condenser and exv
(see scheme below). The refrigerant flow through this exchanger for motor cooling purpose is controlled by a
thermal expansion valve. The opening of this valve is done by heating its internal resistor via 24 vac ouput signal
from the screw compressor board, channel 13. For circuit which has 2 compressors, an additional solenoid (see
scheme below, x=a for circuit A, x=b for circuit B) shall be controlled to balance motor temperatures. These solenoid
output are located at channel 14 of the screw compressor board.
4.7.1 Motor Cooling Control with TQ feedback Signal Control
(refer to factory configuration and wiring for retrofit, pages, 21, 23 and 24)
Tq valve opening position depends on the heat (resistor is the image) on the TQ valve and also the equali-
sation pressure located at plate exchanger (in our application, quite the same than economiser pressure).
With the same economiser pressure, the higher heating signal is commanded (CPA1_PUL, or
CPB1_PUL), the lower is the resistor and the more the valve is opened.
With same heating signal value, if the economiser pressure increases, the valve will tend to close. And
vice versa
Based on this relation, if the feedback signal is enabled, the control will check all the time the relation TQ
position = F (economiser pressure/TQ resistor) and shall make a kind of override (absolutely required at
the start-up, resistor is very high)
When a value of 200 is sent on CPA1_PUL or CPB1_PUL (hardware SIO variable) some time, that means
resistor value is a little above the minimum position, preheat is sent.
This value is sent also when loading capacity.
When the economiser pressure is steady, and TQ resistor is near to the pre-opening position, regular
control (PID) is used.
TQ resistor sensor is connected to the EXV board. The value read is in K Ohms MTQ_RESA (for circuit
A), MTQ_RESB (for circuit B). During regular operation, value read shall be from 0.7 k Ohm to 4 k
Ohms.
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CARRIER SA
30GX&HX PRO_DIALOG 4 V.2
Condenser
sub-cooling
Evaporator
EXV
NOT TO BE DISCLOSED TO PERSONS OUTSIDE CARRIER ORGANIZATION
manuals search engine
USER'S GUIDE FOR
plate exchanger
motor cooling valve
C
©
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ARRIER S A
ECG-UG-02-002
Page: 37/98
Rev: Original
compressor 1
cpx1_mc2
compressor 2
cpx2_mc2