Lennox L-series

[fitzyfitta]

I have a LGA120HH2y giving me an error code 4. Which is A17 input indicates smoke alarm. I located both return and supply air smoke alarms. Both checked out ok and are showing me green led as their manual states. I was looking to see if their is anyway to bypass the smoke alarm in the units programming. I tried unplugging their molex plugs but still recieve the error code. I'm going to test the smokes with the magnet but am at a loss right now. Any input is always appreciated.

[timebuilder]

Find the input that goes to the A55 board, the IMC, and test for voltage at the proper terminals to see if one of those detectors is in trouble. You can easily have a bad contact in the detector even though the green LED is lit.

[valdelocc]

I believe Lennox are wired to the normally open contacts in the smoke detector, weird that you pulled the the plug and it didn't clear the code, there is no way to bypass that in the ECTO.
Some of the old System Sensors detector were notorious for failing with green LED on.

[coolerik]

You sure u cant dissable in the a55 ecto paramaters? Isswear i saw it in there somewhere... dont havethe book infront of me, im probably wrong

[valdelocc]

You sure u cant dissable in the a55 ecto paramaters? Isswear i saw it in there somewhere... dont havethe book infront of me, im probably wrong

I'm pretty sure u cant disable it, u can change how the unit responds the fire alarm; unit off,blower on, exhaust off etc. but the unit will not function.

[coolerik]

I'm pretty sure u cant disable it, u can change how the unit responds the fire alarm; unit off,blower on, exhaust off etc. but the unit will not function.

Gotcha... i hate f'in around with ecto paramaters

[fitzyfitta]

I just read the manual for the third time and it does appear that you can change the parameters but unable to disable the smoke detectors. I tried Lennox tech support for some help but after almost 90 minutes on hold my cell died and I called it a day. I'm going to try timebuilders advise and will keep you guys posted. Thanks for the responses.

[slctech]

Like most manufactures, Lennox uses Sensor System RA and SA smokes. Here is a publicly available guide direct from Sensor System's site. This may help in determining if it is actually the smoke contacts.
I have never seen the Lennox IMC internally fail on a smoke issue. I would concentrate on the smokes themselves or the wiring to the IMC board. The IMC is just monitoring whether the NO contacts on the smoke have closed. If there was actually a smoke related issue the NO relay will close the loop and the IMC will produce the alarm and follow the programmed ECTO parameter.
With Lennox, on the Smoke module should have constant 24 volts across terminals 9 & 10. And the NO contacts, terminals 6 & 17, should obviously be open.
Should be NO all the way back to the IMC.

http://www.systemsensor.com/pdf/I56-2967.pdf

[fitzyfitta]

Went back today and checked for power at the A17 input ( pin 8 on plug110) and found 24v which indicates a smoke fault. Both smokes are blinking green, but I'm getting no voltage across the n/o contacts 6&17 meaning it's contacts are closed. I then put the magnet on it and initiated test mode. The red led came on and contacts stayed closed. 2 bad smoke detectors??
This unit does server a science lab in a high school. The filters were plugged and the evap coil was nasty. It looks like it may have gotten hot in the blower section. There were some wires that looked almost melted that we're laying on the plastic sample tube on the s/f smoke detector. I have 2 new sensors on order.