King Air e90 environmental system problem

Hopefully someone has experienced this problem before. The system will operate in auto mode. This model has the cockpit and cabin auto modes. Will not work in either mode. Heat/air works fine in manual but not auto. Would welcome any thoughts. Thanks

First off, troubleshooting this depends on the serial number. Different LW planes have slightly different systems. Being that you have cabin controller option, I’m assuming you your SN is between LW-1 and LW-119

With the manual system working fine, my recommendation would be to check the cabin temperature sensor. There is a test procedure in the MM that spells out how to do this. You can calibrate the sensor, calibrate your cabin air temp gauge, and check for the specified resistance in the control box.

If that all checked out good, I would look at the schematic for the wiring that is part of the automatic system and start ringing it out for continuity.

Chapter 21-61-00

It’s been my experience that the “Auto” mode on King Airs is pretty unreliable.

LW-47. We have checked all that you mentioned. One thing we found is that a fan up by the temp. sensors was not working. Replaced it and it still does not work. I guess we will start tracing wiring. Thanks for your help.

This might be off topic- but in the lear we never use auto. It is a crap system that never works

Agreed!! Lear, Citation V, CJ3 & E90 sn-LW117 have all had better results in manual for this pilot.

I’d just use manual or start chasing wiring.

In a CJ my friends had the door light that would come on in flight. Turn on the cabin fan, light would go out. Reason - Loose ground wire was attached to fan housing, fan vibration completed the circuit.

Thanks for the comments. We will keep looking for the problem, but looks like manual is my better option based on y’alls experience.