Exhuast Fan Failure:

Problem: There is no exhaust airflow indication after the exhaust fan has been requested on.
Check: Check belts, linkages, etc. on the Exhaust Fan assembly. If these are
ok, check field/unit wiring between RTM and Exhaust Fan. If Exhaust Fan will
run in service mode, then verify airflow proving switch and wiring.

The unit has power exhaust and the Exhaust Proving input is detected OPEN for 40 continuous seconds during any period of time in which the Exhaust Fan binary output is ON.

check 2 things, the proving switch and the 90 degree tube. the tube needs to point directly at the fan wheel and into the on-coming air flow. Trane did a really dumb thing when they designed this part. when the switch is electrically open (no air flow) there will be 24 VAC going to the switch, from the board. when the switch is closed, the 24 VAC is returned to the board...now here is the stupid part...the return terminal on the board is grounded. because the return terminal is grounded, the 24 VAC from the board is grounded out and so it goes to 0 VAC. the board interprets the 0 VAC as a good fan.

i do not know what a "Static PSI Failure" is.

Supply Air Temperature Sensor Failure:

Problem: The Supply Air Temperature sensor input is out of range.
Check: Sensor resistance should be between 830 ohms (200 F) and 345.7Kohms (-40 F). Check field/unit wiring between Sensor and RTM. The unit is reading a signal that is out of range for the Supply Air Temperature input on the RTM (Temperature < -55 F or Temperature > 209 F).

with the exception of the "Static PSI Failure", the other two sensors are connected to the 1U48 board, so you may want to check that out.

good luck.

 

Thanks for the input.

''Static pressure sensor failure" is the other diagnostic.

Both transducers are good as well as the calibration solenoid.

I assume that any of these diagnostics will not allowthe U52 board to send a reference to the exhaust VFD?

The power exhaust runs fine in Service. I have gone through the cabling as you said and will check the other things you mentioned.
Really appreciate the help.

 

atmosphere
The Exhaust Fan Fail diagnostic will be seen whenever the RTM has told the exhaust fan to start but the exhaust fan proving input is still seeing an open proving input after 40 seconds. This diagnostic is ignored in the service mode, that's why the exhaust fan runs in service mode OK. The proving input is 24VDC (measured to ground) when open, and 0VDC when closed. You may find the exhaust fan switch is not closing when the exhaust VFD is running at 22Hz. Others have remedied this by increasing the minimum speed to 30Hz or so, or you can play with the 90 degree pickup tube location to get a little more pressure. Tee in a Magnahelic to see what kind of pressure you are getting. The closing pressure is printed on the switch.

In case you do not have a VFD, look for a plugged tube or bad switch.

Static Pressure Sensor Fail - is that building pressure sensor or duct pressure? To troubleshoot, put a low range Magnhelic (digital is best) in parallel with the transducer high and low ports to see what pressure is seen by the transducer. Measure the transducer output voltage; .25VDC is 0", then it is 0.75V per inch of pressure.


Good Luck

 

Thanks all for the help. Found that the tubing to the transducers, the calibration valve, and the bird feeder had been rearranged by the in house techs. I should know by now to assume nothing when finally getting called out to sort out a mess.

Appreciate the help.