Microtek MHP1-HD Installation Manual download pdf (Page 62)

62 OMRCPMICRO

Erroneous temperature readings and/or "Bad Lvg WaterSen" alarm condition

If it is suspected that the controller is operating using erroneous temperature data or the control sensor alarm

has tripped, the following procedure can be used to check for problems:

1. Remove power from the controller by opening circuit breaker CB1. Verify that the ribbon cable

connections between the controller and the keypad/display and the controller and the ADI board are

proper. Look for bent pins. After reconnecting the ribbon cables, restore power to the controller.

2. Measure the temperature at the suspect sensor location using an accurate thermometer.

3. Determine the sensor's associated terminals on the ADI board. Refer to the panel wiring diagram.

4. Remove power from the controller. Remove the white cap covering the IDC connectors which connect the

sensor wiring to the ADI board. Unplug the red IDC connector block from the ADI board and measure the

resistance across the conductors. Using the thermistor chart (Table 1), compare this value with the

measured temperature.

If the measured resistance and temperature match, go to step 5.

If the measured resistance and temperature do not match, either there is a wiring problem or the sensor is

defective. Check the sensor circuit wiring and connections for defects.

5. Re-insert the IDC connector onto the ADI board and restore power to the controller. Measure the DC

voltage across the metal portion of the IDC connector. Using the thermistor chart, compare this value with

the measured temperature.

If the measured voltage and temperature do not match, the ADI board or the ADI board-to-MCB ribbon

cable is probably defective.

If the measured voltage and temperature match, the MCB is probably defective. The above steps ruled out

problems with the sensor, the sensor wiring, the ribbon cables and the keypad/display.

Erroneous pressure readings

If the evaporator or condenser pressure reading, as read through menus 5 and 6 on the keypad, appear

erroneous or unrealistic, or if the alarm conditions of "Bad Evap PresSen" or "Bad Cond PresSen" are logged,

the following procedure should be followed to check the pressure transducers:

1. Check for proper ribbon cable and other connections.

2. Measure the voltage (0 to 5 VDC) across the suspected pressure transducer at ADI Board terminal A1,

A2, A3 or A4, whichever applies.

3. Compare this reading with what the value should be according to that shown in Figure 3 and Figure 4, the

transducer output characteristics (see note below).

4. Check for 5 VDC at terminal 214 as supplied by the MCB and also at the MCB itself.

If the voltage is 5 VDC in both places, the sensor is probably defective.

If the voltage is not 5 VDC at terminal 214, check wire 820 to the MCB for shorts or scrapes.

If the voltage at the MCB is not 5 VDC, check wiring between the MCB and T2. There could be shorts or

other wiring problems from the incoming power. Refer to "Troubleshooting Power Problems" under the

troubleshoot section for the Microprocessor Control Board.

Note: The actual pressure to the transducer must be known. Install a pressure gauge on the circuit

to verify pressure. If that transducer is not defective, then it is likely that the ADI board itself is

defective and must be replaced, or the refrigerant charge may require attention.

Freezestat alarm condition

The MicroTech "Freeze Stat Prot" alarm condition can occur due to several factors. Following is a list of

different suggestions on items to inspect or set points to adjust when the alarm occurs frequently. The

suggestions do not have to be performed in sequence as they are in no particular order.

1. Check the set points for the "LP CutIn", "Frz Stat" and "Frze H

O" on Menu 22. They should be adjusted

according to the individual job. If the job includes glycol, it is a low temperature job and/or is an ice job,

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Microtek MHP1-HD Installation Manual Page 62

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