McQuay IM 660-3 13
Service Information
Erroneous Temperature Readings
If you suspect that the WSHP controller is operating using
erroneous temperature data, check the sensors using the
following procedure:
1 Measure the temperature at the suspect sensor using an
accurate thermometer.
2 Determine the sensor’s analog input number. Refer to the
unit wiring diagram or to the input/output tables (Table 10).
3 Remove the connector from its WSHP controller terminals
and measure the resistance of the sensor (through the
sensor connections).
4 Using the thermistor chart (Table 11), compare this value to
the measured temperature.
5
If the measured resistance and temperature match, the WSHP
controller may require factory service, or it may be defective.
6 If the measured resistance and temperature do not
match, either there is a wiring problem or the sensor is
defective. Check the wiring connection and the sensor
circuit wiring for defects.
Digital Input Faults
A digital input fault usually is caused by high-pressure,
low-pressure or low-temperature alarm conditions resulting
from mechanical problems in the water source heat pump. It
also can be caused by a problem in the digital input circuit.
Below is a procedure to use to check for problems in the
digital input circuit. If the probable cause of the fault is found
using this procedure, attempt to clear the fault by cycling
power to the WSHP. If the probable cause of the fault is not
found using this procedure, assume that mechanical problems
exist and have a qualified technician service the unit before
attempting to reset the WSHP Controller.
1 Check the voltage at the secondary of transformer; it should
be approximately 24 VAC.
2 Determine the switch’s digital input number. Refer to the
unit wiring diagram or to the input/output tables (Table 10).
3 Check the wiring and connections throughout the digital
input circuit.
4 Measure the resistance through the switch contacts (with at
least one wire disconnected). The switches normally are
closed.
Brownout Fault
The WSHP controller senses the AC voltage at the power input
section terminals J41 and J42 (see unit wiring diagram). If the
voltage at these terminals is less than 19.68 VAC for at least 1
second, the brownout fault occurs. The fault automatically
clears if the voltage at the terminals remains greater than 21.6
VAC for at least 1 second.
If a brownout fault occurs, check the line voltage to the water
source heat pump. If it is less than 82% of the nameplate value,
contact the power company. If the line voltage remains greater
than 90% of the nameplate value for more than 1 second but
the fault does not reset, perform the following procedure:
1 Measure the voltage between terminals J41 and J42 on the
WSHP controller.
2 If the voltage is low or fluctuates around 19.68 VAC, the
WSHP controller is functioning properly. Go on to step 2.
3 If the voltage remains above 21.6 VAC for 1 second but the
fault does not reset, the WSHP controller is defective.
4 Check the primary and secondary voltages of the power
supply transformers.
5 Check for faulty wiring or connections throughout the
power supply circuit.
WSHP Controller Replacement
Data relating to the water source heat pump controller
configuration and characteristics are stored at the factory when
each unit is built and tested. If a WSHP controller is defective
and must be replaced, its unit-specific software (defined by the
above data) must be loaded into the replacement controller at the
factory. To do this, the factory needs the following information:
• Full model number
• Serial number
• Date code for time of manufacture
• Software version of code loaded in the controller
The unit model and serial numbers are listed on the unit
dataplate. The date code and software version of code are
printed on the MicroTech unit controller adhesive-backed
label. This information must be included with the replacement
WSHP controller part order.
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