Blower fan runs constantly

epowerfan

I tried gently smacking the htg fan relay and it did not click. Also it doesn't move when the fan starts OR stops from the access panel interlock switch.

I tried to gently pry the HFR out of it's socket to inspect it-- no go so I didn't force it. Can this relay just unplug from a socket? Is it locked or soldered in? Printed on relay is:

Potter & Brumfield
KU-6454
24V 50/60 Hz
10 FLA 30 LRA 125VAC
5 FLA 15 LRA 250VAC
728-0016

The wiring diag says the HFR is normally closed. I figure it's wired normally on, and another component in the wiring control is making it stay it on-- like maybe the high limit switch.

X47, do we have the same model furnace?

Is the high limit switch a 2-position thermostat, N.O. at lower temp and closed upon higher temp? Purpose to keep the blower running after the burner shuts off, until the temp cools down enough?

I unplugged the power to the furnace and measured resistance across the terminals of the high limit switch. .2 Ohms while about 65 deg F-- if it's a 2-position stat, it's closed.

Btw Chris, my Tstat has a button to man turn on and off the fan only, but not to schedule running just the fan.

The high limit switch has the following markings:
STEMCO
430-1457
HH12ZA174C
L170 9030

epowerfan

More stupid questions. How do I replace the fan control relay? Just tug harder on it, and it comes out of a socket on the control board?

At this point I suspect the htg fan relay; or possibly the fan hi lim control. Maybe I can take them to Johnstone Supply and get replacements?

Any advice is appreciated. Thanks, Mark

Attached Images

 

epowerfan

Called Tycoelectronics (P&B) about replacing the relay. They said that part# (KU-6454) was custom; it could be plugged into a socket, or also might have a threaded stud bolting it in.

All power off, removed the board screws and looked at the back side. No threaded stud securing the relay.. but it looks like the board doesn't have a socket, like the relay prongs are just soldered in the board.

Any advice on next step? A way to test the relay?

A way to test the Stemco hi limit control?
-Mark

hvaclover

That relay is soldered in.

When wa the last time you changed filters.?

__________________
Just slow, not stupid.

kennzz05

you need a board they are non repairable the cost is about 50 dollars again if you still have heat limits are ok

epowerfan

I remember changing filters early summer. They look fairly clean. Is there another safety that might have tripped if they're dirty?

Where can I buy a replacement board?

TG the unit is still functional. I've done a lot of soldering, so willing to remove the board and put in a new relay. Know of a way to test if the relay is bad?

Anyone know how to test the hi limit control?

-Mark

kennzz05

dude:if you have heat the limits are good ok, im 100% positive many supply houses sell an aftermarket board give them the number on the board I believe that board is referred to as a (16) board the last numbers in the model number but it should be available at other than carrier dealers although you may have trouble getting them to sell it to you as a homeowner and not a technician


and to repeat if theres a flame than all your limits are closed open limit=no heat

epowerfan

Thanks dude ,
Based on the relay observation & whack test, and blower fan stays on, would you say my HFR is bad? Unusual to solder on a replacement relay?

Are you saying we can rule out faulty limit control as cause of the blower staying on longer than it should? Just asking- I asked how the hi lim works, and no answer yet.

What are some possible supply houses for an aftermarket board?
-Mark

hvaclover

Try Googling. Do you think he lives in your town.

__________________
Just slow, not stupid.

x47

epowerfan,

I have a Carrier furnace Model #58SE075-3, I see a date of 1975.

As I mentioned above, I jumped and disconnected the high limit switch (#HH12ZA251), but the fan kept running when jumped or disconnected, so I assume that the switch is good.

The control board is 302075-302.

After perfomring the test advised by Kennezz05, it was obvious that the fan relay was the problem. I replaced the board and everything is functioning as normal.

I used replacement board # ICM271. I found the correct board by googling my control board part number, which is visable on the front of the board. That gave me a cross reference which ultimately cross-referenced to ICM271. It was $40 on ebay an I got it in 2 days.

Hope that helps

epowerfan

Thanks x47, that helps a lot.

I did your test of the high limit while plugged in w/ same result-- open or closed, it did not stop the constant blower. Also while the unit power was on, I measured zero Volts across the hi limit, so I guess it is an ON-OFF Tstat.

I tried whacking the HFR a bit more firmly (Tstat in OFF, while the panel interlock sw depressed and blower starting). The HFR still didn't budge, but the CFR contacted & shut down the blower. In this state I turned the Tstat to heat mode and moved the setpoint up for heat. I heard the small click that's usually followed by clicking of the ignitor, but no ignitor and the blower didn't start.

So it would seem my HFR is bad, or something else on the board. Putting labels on the connected wires before I remove the board to get it's numbers.
-Mark

kennzz05

yaknow not to be a douchebag but if you had followed the advice given you by the techs that have something like 90 years of experiance between us and gotten the board a couple of days ago youd have heat today if hvac was YOUR field of expertise you wouldnt be on here asking

epowerfan

Not dbag, I appreciate your experience & advice.
True, hvac isn't my field and I didn't know you all were so many yrs expd techs. So many Qs cuz I want to understand more details of how the unit works and precise troubleshooting than needed to fix it this prob.

Fortunately I never lost heat; just keeping the access panel ajar when not using until proper fan control is back. And I only want to fix what's broken, so if replacing the relay works I'll keep the board.
Thanks, Mark

hvaclover

Then don't bother the techs if you are not willing to follow the advice given.

You cannot just selectively repair the electronics that fail. The parts are approved by agencies that certify the safety of the unit.

You are trying to circumvent the very system that makes your furnace safe. Follow the previous advice or move on.


Mods if you feel this is too harsh than by all means delete it. But the OP
has been given more than enough info to to solve his issues bur will not
listen.

__________________
Just slow, not stupid.

epowerfan

Hvaclover, Thanks again for the good advice. Sorry if I bothered you.