We have a Carrier RTU model# 48DJD028 from 1995 in which every part in the heating section has recently been replaced. Heat exchanger, inducer motor, burner, ignition module, flame sensor, cables, collector box, pilot runner and gas valve. The unit had been online with the proper manifold pressure for two weeks with no issue. Today there was a no heat call on the unit. The unit would come on and establish pilot flame but never generated the proper MV signal to switch over to the main valve. The ignition module is a United technologies model# 1003-600a, Carrier part number LH33c7010. The instruction manual says that it needs a min. of 0.3 MV to switch over. I normally see with this module a little over 1.0 With everything I tried the reading was 0. I cleaned the brand new sensor, ohmed the cable out, try a completely different flame sensor, and still nothing. I tried running a common ground from the pilot burner, then to the module, and then to the main unit's ground. Still a reading of 0. I tried reversing the placement of the spark ignitor, and the sensor (one is on one end of the burners, and the other is at the other end of the burner) still nothing. You can actually see the pilot flame enveloping the flame sensor, and the sensor turning red, but still no MV reading. It's strange that the unit started up fine when all these parts were replaced, and lasted two weeks and now it will not switch over to the main valve at all. I also tried adjusting the pilot regulator in the gas valve, with no change. The sensor sits about 1/8" over the pilot runner, and is not touching any ground. Any help or suggestions would be much appreciated. Thanks to all
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