Service manual

A DJM3.2 MANUAL
Discharge Sensor Calibration
The discharge sensor this control is based on is the Johnson Control TE 6000-960, or equivalent.
(Refer to diagram on Page 23.) Above is a chart to determine if the sensor itself is accurate.
NOTE: These controls are calibrated at the factory and in most instances field calibration
is not necessary. The discharge sensor is used for both temperature control and
low limit safety control. For that reason it is VERY important for this
calibration step is PROPERLY done. The DJM3.2 has two calibration pots. Pot
D Sen Cal is used to calibrate the discharge sensor, and Pot Dis SP Cal is used
to calibrate the discharge set-point.
1. Accurately measure the discharge air temperature at the temperature sensor.
NOTE: The sensor should be located in a stable, non-changing temperature location
between 5 and 30ºC.
2. Read the DJM3.2 discharge temperature by reading the voltage across resistor R29 (see diagram
Page 23). The ¼ watt, 1820 ohm resistor (colour code = brown, gray, red, brown, (brown or red)) is
located next to terminals M and Q. DJM3.2 controls built after the fall 1995 have terminals to aid
in this reading.
With the voltmeter set on the 20 VDC scale measure the DC voltage across R29 (the negative meter
probe goes to the resistor lead closest to terminal Q). The readings are based on 10ºC per volt.
A reading of 0 volts = 0ºC. A reading of 2.15 volts = 21.5ºC.
TEMPERATURE READOUT FROM VOLTAGE ON READOUT PINS (See diagram
Page 23)
Voltage (VDC) ºC ºF
1 10 50
1.5 15 59
2 20 68
2.5 25 77
3 30 86
3.5 35 95
4 40 104
NOTE: The readable range is 0 to 55ºC. At higher temperatures the reading accuracy is
reduced. Typically at 50ºC the reading will indicate 2-3ºC lower than actual.
If the discharge sensor needs calibration, adjust Pot D Sen Cal (located next to terminal S) until the
actual temperature reading on R29 agrees with the temperature reading taken at the sensor.
Discharge Set-Point Calibration
1. Record the settings of dipswitches 1, 2, and 3.
2. Turn off dipswitches 1, 2, and 3. If the “OR” terminal is used, the wire to terminal “OR” must be
removed.
3. Set the discharge set point to 21ºC. To calibrate the set point, the calculated operating set-point
(SPC) must be known. Turning the dipswitches off eliminated all the resets and the remaining SPC
value is the dial set point. (SPC = Dial set-point + reset.) The SPC can be read using a DC voltmeter
connected across resistor #R124, ¼ watt, 1210 ohms (colour code = brown, red, brown, brown
(brown/red)). This resistor is located next to the R29 temperature readout resistor but is slightly
further from terminals M and Q than R29 (drawing Page 23). The negative meter probe goes to the
resistor lead closest to terminal Q. The Calculated set-point resistor readout uses the same 1 volt
Page 25 Revised: 3/11/99