Differential Pressure Switch Set Point And Null Span (Units Equipped With Modulating Power Exhaust Option); Vav Diagnostic Information - Carrier 48DK024 Controls Operation And Troubleshooting

Differential Pressure Switch Set Point and Null
Span (Units Equipped with Modulating Power
Exhaust Option) —
The set point range for this switch
is −0.5 in. wg to 0.5 in. wg. Factory setting is
To adjust set point, turn set point adjusting screw (See
Fig. 31) clockwise to decrease set point and counterclock-
wise to increase set point. This switch also has an adjustable
null span. The null span is the pressure change that can be
made without contacts opening or closing. It is adjustable
from 0.06 in. wg to 0.14 in. wg when set point is at mini-
mum position (−0.5 in. wg) and 0.07 in. wg to 0.14 in. wg
when set point is at maximum position ( 0.5 in. wg). To
adjust null span, turn null adjusting screw (Fig. 31) clock-
wise to decrease span and counterclockwise to increase span.
All switches leave factory with null span set at maximum
position. The smaller the null span, the closer the pressure
will be maintained to desired set point.
VAV Diagnostic Information —
sor contains extensive self-diagnostic information. The 2-digit
LED display is used to display the diagnostic codes and the
alarm light (located next to display) is energized whenever
a diagnostic code is tripped. When a problem is suspected,
always check the display first for diagnostic information.
Table 12 details diagnostic codes and a brief description
of the possible causes.
NOTE: Codes 52-54, 56-58, 61, 62, 65-69, 73, 74, and 77-80
are not used on these units.
IMPORTANT: The microprocessor memory and the
display will be cleared if the power to the microproces-
sor is shut off. DO NOT attempt to bypass, short, or
modify the control circuit or electronic boards in any
way to correct a problem. This could result in a haz-
ardous operating condition.
DISPLAY DESCRIPTION OF FAILURE
51 Compressor 1 failure
55 Compressor 2 failure
59 Loss-of-charge circuit 1
60 Loss-of-charge circuit 2
63 Low oil pressure circuit 1
64 Low oil pressure circuit 2
70 Illegal unit configuration
71 Leaving-air thermistor failure
72 Entering-air thermistor failure
75 Circuit 1 Resistor (024-030)
Circuit 1 Saturated Condensing Thermistor (034-074)
76 Circuit 2 Resistor (024-030)
Circuit 2 Saturated Condensing Thermistor (034-074)
81 Reset temperature thermistor failure
82 Leaving-air set point potentiometer failure
83 Economizer potentiometer failure
84 Reset limit set point potentiometer failure
85 Demand limit potentiometer failure
86 Minimum economizer potentiometer failure
87 Warm-up set point potentiometer failure
NOTES:
1. Illegal unit configuration caused by missing programmable header or both unloader DIP switches on.
2. All auto. reset failures that cause the unit to stop will restart when the error has been corrected.
3. All manual reset errors must be reset by turning the control switch off and then back on.
4. Valid resistance range for the thermistors is 363,000 to 219 ohms.
5. Codes 52-54, 56-58, 61-69, 73, 74, and 77-80 are not used on these units.
0.1 in. wg.
The microproces-
Table 12 — Overload Codes
ACTION TAKEN
BY CONTROL
Circuit 1 shut off
Circuit 2 shut off
Circuit 1 shut off
Circuit 2 shut off
Circuit 1 shut off
Circuit 2 shut off
Unit will not start
Unit shut off
Use default value
Unit shut off
Unit shut off
Stop reset
Use default value
Close economizer
Stop reset
Stop demand limit
Close economizer
Use default value
23
CODES 51 AND 55: COMPRESSOR FAILURE — If con-
trol relay (CR) opens while compressor should be operating,
compressor will stop and microprocessor will energize alarm
light and display a code of
pressor) when display button is pushed. The compressor will
be locked off; to reset, the ON-OFF switch must be turned
to OFF and then to ON position.
Code 51 is for compressor 1, and Code 55 is for com-
pressor 2. Other codes are not used for 024-074 units.
The microprocessor has also been programmed to indi-
cate a compressor failure if CR switch is closed when com-
pressor is not supposed to be on.
If a failure occurs, the following are possible causes:
High-Pressure Switch Open — The high-pressure switch for
each compressor is wired in series with 24-v power that en-
ergizes CR. If high-pressure switch opens during operation,
CR will stop compressor and this will be detected by micro-
processor through the feedback contacts.
Internal Thermostat — The internal thermostat in each com-
pressor is also wired in series with 24-v power that ener-
gizes CR. If thermostat fails or switch opens during opera-
tion of compressor, compressor will shut down and failure is
detected through feedback contacts.
CR Failure — If CR fails with large relay either open or closed,
microprocessor will detect this, lock compressor off, and in-
dicate an error.
Relay Board Failure — If small 24-v relay on the relay board
fails, microprocessor will detect this through feedback con-
tacts and indicate an error.
RESET
METHOD
Manual
Manual
Manual
Manual
Manual
Manual
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
Auto.
51 or 55 (depending on com-
PROBABLE CAUSE
High-pressure switch or high dis-
charge gas thermostat switch
trip, compressor ground current
2.5 amp or compressor board
relay on when it is not supposed
to be on. Wiring error between
electronic control and compres-
sor protection module.
Not used on 024-030 units.
Check jumper on processor
board. For 034-074 units, this
indicates either a low refrigerant
charge, or a loss-of-charge
switch failure.
Not used; Check jumper on pro-
cessor board.
Configuration error (see Note 1).
Thermistor or resistor failure, wir-
ing error, or thermistor or resistor
not connected to the processor
board.
Potentiometer improperly con-
nected, potentiometer setting out
of range, potentiometer failure or
wiring error.