Day & Night BDP Carrier furnace
Model 396JAW036045

System heat cycle works just fine; thermostat calls for heat; fan comes on - shortly thereafter the gas comes on and house heats as expected. Intermittently - but more and more often (close to always now), after the thermostat clicks off, the fan continues to run (and will not shut off). Will run for hours, so I assume forever (just blowing cold air around).

Recently while running (and heat off) I completely disconnected all thermostat wires and the fan continued to run - even with a furnace AC power off/on cycle. Looks to be a control board / furnace issue and would appreciate any pointers that i could check. I have seen quite a few threads where there is no heat - but my heat is fine, issue is Fan not going off as expected.

And yes, it's a 1983 system, but live in Bay Area of CA so it gets very nominal use. Would prefer to get this corrected and let the unit keep on doing it's thing.

Thanks,
-john

 

Sounds like heat relay is sticking. Try tapping on the side of the furnace after it has run for few minutes past the "off" time. This is quite common. Repair is a new board if this is the model I'm thinking of.

 

Thanks mbk3,

tried the side of the furnace wrap to no avail. Also pulled to door and over-rode the cover switch and directly tapped the two relays (was not sure which one was the heater). Also no effect. May go the control board route - AMZN seems to have ICM boards at reasonable prices.

One question - saw an old thread and there was a comment about a fuse (link?) on the board that may be a cause. No of such a fuse?

 

You other option, which may not be to your liking, is to let the furnace fan run. I have left my furnace fan in the on position since I moved into the house (10+ years). The fan helps with overall circulation of the air and filtering of any crap that floats around. Running the fan full time is also better for the motor (think highway vs city driving). Doesn't solve your problem of the motor not turning off, but it may not be that much of a problem if you just leave it on.

 

An open fusible link would incur continuous blower operation, however the burner would not come on.

 

Ok, an interesting update - not what I hoped for, but wanted to update the thread none the less.

Purchased an ICM271 controller from Amazon and installed per instructions and other posts on the net. There were no cut jumpers or changes from a review of the old board and the new one that I could tell) - so installed as it came w/o mod.

Turned on the gas & power and unlike before, the fan did not turn on immediately (yeah). Used the thermostat to call for a heat cycle and the pilot lit and then shortly thereafter the 3 burners got gas. However after more than 4 minutes the fan did NOT turn on. The gas turned off (assume a safety limit kicked in?) and immediately after the gas was off the fan kicked On. Fan ran for 30 seconds or so and then turned off. If i let the thermostat stay in the call for heat state, the process would repeat.

Checked the wires on the controller to make sure all are solid and correct (labels are still on them) and no change when i tried again. So then went to the thermostat and turned the fan on for a 15 min timer - and then called for a heat cycle. This time it went pilot, gas and then it continued to operate as one would expect (I assume because the fan was running manually). Turned the thermostat down, gas kicked off and then i cancelled the manual fan timer.

So the fan operates - just not automatically at the beginning of a heat cycle (sound right?). Any ideas - i feel closer but hate having a 'new' issue.

Thanks all,
-john

 

Are you sure you have the proper board? Also is the heat speed wire on the proper terminal. Some boards have a "park" position for unused motor speed wires.

 

MBK3,

The ICM271 paperwork says that it replaces HH84AA011 board (the original). Now the new one is labeled as HH84AA020 - and they state it replaces 10/11/12/13/20 boards. Also, i saw a positive review (maybe fake?) where the reviewer said it worked perfectly for an 11 bo.ard replacement. So i think i have the correct board.

not sure i understand the heat speed comment. There are the exact # of spades as the original, so every wire is on a lug and no empty lugs. I did note that the only spade not in essentially the exact same position was HI & LO were swapped location-wise (they are right next to each other). Doing some debugging after i posted here, i swapped HI & LO - no difference in behavior.

Lastly, the troubleshotoing instructions that came with the install instructions indicated to check the following if no fan output in heat mode:

- 24V from R to C (correct)
- 24V from W to C when thermostat calling for heat (correct)
- 24V from Gas 1 to C and 24V from Gas 3 to C
- Gas 1 had 24V when the ignitor was On
- Gas 3 had 24V when the burners kicked On - so i assume correct (they did not state the condition for the 24V test)
- check fan connections at LO 7 COM (not sure what this means)
- Verify low speed fan operates correctly (do not know how to verify this)

-john

 

UPDATE:

I can't attach the 2 page pdf for the replacement board but a url for it is here -- http://www.icmcontrols.com/ProdImages/ig_LIAF044-1.pdf

In reviewing it again, and finding a more detailed 8 page manual online, i noticed the blower operating mode table was a bit confusing. And while the original board did NOT have any jumper cut - it looks like I may have to cut R17 jumper.

What I did do just now was to disconnect the Y cable at the thermostat. When i did this the Heat On and Heat Off cycle operated as expected.

So what i hope is one last question to the forum here. What does a Y wire do for a heat only furnace? I thought Y was for cooling.

Almost there i believe,
-john

 

Yes it is. Y goes to the condenser which you apparently don't have