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Blower fan runs constantly

44K views 67 replies 12 participants last post by  ahome3688 
#1 · (Edited)
I've got a Carrier downdraft htg/fan coil unit, 1990 Model No. 58DRC080-JB.

Unit was working fine. Last weekend main power to the house went on and off about 5 times in 1 hour. Next morning the blower kept running even after the heat setpoint was satisfied (and burner properly cut off). I made the blower stop by opening the access panel to trip the safety switch.

To test for Tstat damage I completely disconnected the thermostat wires - The blower still runs constantly when the panel door closes, so I think Tstat isn't the problem. Heating and cooling both function properly from the Tstat, just that the blower stays on constant; I have the access panel ajar until I want to run it.

Looking at the unit and the wiring diag inside the panel, I wonder if there's an airflow safety switch or temp safety that got shorted out.

Anyone heard of power outage causing a fault like this before?

Thanks in advance for any ideas on troubleshooting, or other advice.
Made the mistake of asking on hvac-talk forums, just for any known DIY sites for homeowners, and within mins, a handful of unfriendly posts and the thread was closed. :huh:
-Mark
 
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#7 ·
Emergency switch?

Thanks guys-- that's at least 2 possibles to investigate.

The fan control button on the programmable T500 electronic Tstat is def. not on. I don't know what an emergency switch is. Wish I had an electronic version of the wiring diag to share-- any chance I could find one on the web?

There are 2 relay/contactors in clear plastic cases inside the unit's main control box-- labeled HFR & CFR on diag. The htg fan relay says N.C. spst, the CFR just says dpdt.

Below the fan and above the burner are a gray box Ignition Lockout (flowswitch?) and a black-back thing that looks like it might be a temp sensor.

Now this is odd... last night I ran the htg and when the setpoint was satisfied, the fan went off normally on it's own. I thought it had worked itself out and I was home free. But this morning, after htg came on auto by Tstat program, the fan stayed on constant again after the setpoint was satisfied.
So I'm back to access-door ajar to keep the fan from running.
 

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#8 ·
I have the same problem

I have the same problem as epowerfan - fan doesn't turn off - the only way to turn off the fan is to switch the furnance master switch on the wall.

I jumped the high limit switch as well as disconnected it - no effect on the fan. Thermostat fan switch is on "AUTO".

Is it worth replacing the control board (about $40 online) or is this something that a service tech needs to diagnose?
 
#9 ·
x47-- high limit switch? Temp hi lim? airflow switch? and where is it? Could mine be one of those in the picture?

I watched the HFR & CFR while i closed the access panel interlock switch. As the blower started I didn't see either relay close.

What gives?? Does that mean my Htg Fan Relay is normally closed like the wiring diag says.. and a N.O. temp limit switch is in series with it, so that the blower is ON unless a temp safety switch is below setpoint temp?

-Mark
 
#10 ·
if you still have heat (which means hi limits are closed and not the prob) and you arent getting any lo voltage sig at the low volt term on the board (G) than id say its the board pull the low speed fan wire see if it shuts off you might also try gently smacking the relay while the fans running
 
#11 ·
high limit switch

the high limit switch is the one on the left in your photo - has 2 wires coming from it. I believe it is normally closed.

I am going to try what kennzz05 recommends - that should confirm whether or not the fan controller board is working right.
 
#15 ·
tapped on the relay - fan has been working fine for half a day. something is probably bad in the relay. I will see how long it goes without reverting to the fan being on all the time.

the points on the relay are pitted and will stick every now and than if it weren't a sealed relay you could sand the points but its pretty much a throwaway item unless you want to try and solder a new relay in but this isn't Russia so we just toss em and replace since its not coming out of our pocket lol :)
 
#16 · (Edited)
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
 
#17 ·
how to replace fan control relay

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
 

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#18 ·
update

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
 
#19 ·
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
That relay is soldered in.

When wa the last time you changed filters.?
 
#21 ·
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
 
#22 · (Edited)
:eek::eek: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
 
#23 ·
Thanks dude :thumbsup:,
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
 
#25 ·
It was my control board

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
 
#26 ·
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
 
#27 ·
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
 
#28 ·
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
 
#29 ·
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.
 
#31 ·
board replaced, now blower won't run

The new board arrived today. ICM271C to replace my CES0110018 printed on the orig board.
I read all the instructions and installed it (w/ 3Amp car fuse in).

Tstat in OFF, plugged in the furnace power chord and pressed the access panel interlock switch-- the blower didn't come on. whew

Tstat to Htg mode and setpoint to bring heat...
The ignitor began clicking in a few seconds as normal, the burner fired.. but the blower didn't start.

Tstat to Clg mode and setpoint for Clg. Within a couple seconds the condensing unit started but not the Blower fan.

Also the FAN button on the Tstat will not start & stop the blower like it used to.

Yikes. Now what? Off to search forum for similar prob. -Mark
 
#32 ·
The new board arrived today. ICM271C to replace my CES0110018 printed on the orig board.
I read all the instructions and installed it (w/ 3Amp car fuse in).

Tstat in OFF, plugged in the furnace power chord and pressed the access panel interlock switch-- the blower didn't come on. whew

Tstat to Htg mode and setpoint to bring heat...
The ignitor began clicking in a few seconds as normal, the burner fired.. but the blower didn't start.

Tstat to Clg mode and setpoint for Clg. Within a couple seconds the condensing unit started but not the Blower fan.

Also the FAN button on the Tstat will not start & stop the blower like it used to.

Yikes. Now what? Off to search forum for similar prob. -Mark

double check your wireing sounds like a bad board read motor terminals on board for voltage when you know it should be present fan "on" for example. (read at hi speed terminal). use tape to hold door switch in (if your not doing that already)
 
#33 ·
Ok, hope I do this right.
First a confession. When I removed the orig board I labeled the green Tstat wire just "G", when it went to either GH or GC. Should the Green wire from the Tstat terminate at GH or GC?

The orig board has a wire jumper (J1) between GH and the R terminal adjacent. The new board has a (JW-1) that looks like some kinda little diode / jumper? I can't tell what it jumps. http://www.icmcontrols.com/downloads/icm271_ag.pdf

Disconnected the HI and LO connectors to the fan. Tsat to Fan ON, pressed the door switch and measured for VAC between HI and COM, and LO and COM.

It read .5V AC HI-COM.

and 2.5V AC LO-COM. (Voltage was same whether the G Tstat wire to GH or GC)

Also the new board Umanual Tshooting says,
No fan output in heat mode: Verify that you have 24 volts between W and C. Check-- 27 VAC
Make sure you have continuity between the GAS1 and GAS3 terminals. I measured .65 K-Ohms between GAS1 & GAS3. **Could this be the problem?

http://www.diychatroom.com/showthread.php?t=13714&highlight=blower+carrier+control
The guy in this thread found a GAS1-to-GAS3 jumper on his orig board. My orig board has no jumper GAS1-GAS3, and I measured 370 KOhms between GAS1 & 3 while sitting on the table.
 
#34 · (Edited)
Ok, hope I do this right.
First a confession. When I removed the orig board I labeled the green Tstat wire just "G", when it went to either GH or GC. Should the Green wire from the Tstat terminate at GH or GC?

The orig board has a wire jumper (J1) between GH and the R terminal adjacent. The new board has a (JW-1) that looks like some kinda little diode / jumper? I can't tell what it jumps. http://www.icmcontrols.com/downloads/icm271_ag.pdf

Disconnected the HI and LO connectors to the fan. Tsat to Fan ON, pressed the door switch and measured for VAC between HI and COM, and LO and COM.

It read .5V AC HI-COM.

and 2.5V AC LO-COM. (Voltage was same whether the G Tstat wire to GH or GC)

Also the new board Umanual Tshooting says,
No fan output in heat mode: Verify that you have 24 volts between W and C. Check-- 27 VAC
Make sure you have continuity between the GAS1 and GAS3 terminals. I measured .65 K-Ohms between GAS1 & GAS3. **Could this be the problem?

http://www.diychatroom.com/showthread.php?t=13714&highlight=blower+carrier+control
The guy in this thread found a GAS1-to-GAS3 jumper on his orig board. My orig board has no jumper GAS1-GAS3, and I measured 370 KOhms between GAS1 & 3 while sitting on the table.
youre not reading resistance only continuity its either open or closed and your reading the limit circuit so its got to be done while installed and wired.like last time if flame starts limits are good
G wire at gc

if flame starts and no fan you either got wrong/bad board


try pulling one of the wires off the limit see if the fan starts as tho the limit opened

wasnt the last numbers in your old board a 16 if so i dont see that board you put the link to as being a replacement for the 16 board ok i see where i got the 16 from it was from the relay nevermind
 
#35 ·
Thanks Kennz, I'll keep the G wire to GC.

I pulled one connector off of the hi limit, and the blower still won't turn on.

I read the manual on my Fluke MM and (duh) set it for continuity w/ beeper. The new board beeps 'closed' as soon as call for fan & push door switch.

What do you think about the GH-to-R jumper on the orig board? -Mark
 
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