User Guide

Preliminary Circuit Analysis

In order to diagnose the system it is necessary to determine certain

values. It is helpful to have a volt/ohm multimeter and a xed or variable

resistance between 1100 and 1300 ohms.

Modulation Function:

If sensed (displayed) process temperature is less than 70ºF, perform

step 1 below, otherwise continue to step 2.

1 Disconnect the sensor wires going to the amplier and replace with

means to obtain a resistance value falling somewhere within the

controllers programmed range.

NOTE: “Max Proc Temp” and “Min Proc Temp” settings are located in the

Diagnostic Menu in the MP2.

R ohms Proc T displayed (approx.)

1100 78

1200 125

1300 172

2 Connect a DC voltmeter to the modulating gas valve or the

modulating gas valve amplier terminals. DO NOT disconnect

existing wiring. OR Activate the MP2’s “Monitor” function located in

the Diagnostic Menu to display the voltage output to the modulating

gas valve.

3 Program the temperature “set point” to 10ºF below the displayed

“process temperature”. The DC volts should read no more than 2

VDC.

4 Program the temperature set point to 10º above the displayed

“process temperature”. The DC volts should read at a minimum 15

VDC or the programmed “Max Value VDC” setting located in the

Operation Menu, whichever is less.

NOTE: Controls programmed with a large Offset Temp or Calibration setting

may fail step 3 or 4 due to one or both of the programmed settings. Re-run

the failed test with a 20ºF set point temperature differential or zero the Offset

Temp and Calibration settings. Make note of the settings prior to zeroing and

return them to their original setting after test.