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Old 09-06-2009, 10:40 AM   #1
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Carrier 58SX Main Blower Turns On Without Command


I have a 20 year old Carrier 58SX100-CC-1 that is giving me problems with the main blower. The original Fan Controller Board relay was clicking while the thermostat was in the AC mode. Removal of the board showed the clear plastic relay cover blacken on one side and the 7 pin edge connector contacts were blacken (not totally burned). Cleaned harness contacts, Purchased and installed new controller board ICM-275 and every thing seemed ok. After a few days of running the AC, I noticed the main blower would come on without the air (Y & G) commanding it. The blower would come on for 60 seconds and then shut off for 120 seconds. This would continue in most cases until I would shut power off to the furnace and reset. I have done alot further checking and will cover some of it breifly. I used an O-scope on points of interest. The 24 Volt transformer output is approx. 26-27 Vac (RMS) with steady 59-60 Hz. Removed all the thermostat wires from the controller board (problem still there). Voltage across Thermal Limit Switch leads are 26 Vac and are still that when the blower comes on. Where I am at now, is the thermostat is not connected, after power is applied to furnace, pretty consistantly two hours later the fan will cycle as described. I do not know if the thermal switch is intermittent, so I tied the Thermal Limit Switch wires together to see if problem still there. I will wait for two hours and see. I have contacted the board manufacture and they do not think it is their board. They think the problem is from outside the board. As of now, I think it is their board. I know the furnace is old but I was hoping to get a few more years out of it (kids in college). Anybody have any further ideas what I might look at. thanks for any input.

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Old 09-06-2009, 11:01 AM   #2
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Carrier 58SX Main Blower Turns On Without Command


Is the new board the exact same numbers as the old board? I know Carrier has a bunch of different boards and some of them are retrofits especially with the CESO series. Carrier is very good at listing which furnaces their boards fit on the installation instructions. I assume the new board has the non glass/plastic relays. If it has that skinny plastic edge connector from the burner compartment down onto the board, carefully remove it/blow it out with dry compressed air and slide it back on. That will self clean the contacts. Had one do some weird biz yrs ago. If the limit control opens then the fan runs to "cool" the heat exchanger is what it is designed for. Post some pics of the burners and inducer fan so we know which model you have.


Last edited by yuri; 09-06-2009 at 11:04 AM.
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Old 09-06-2009, 11:30 AM   #3
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Carrier 58SX Main Blower Turns On Without Command


The old board is a Carrier HH84AA01 and the new board is a universal replacement (so they say) ICM275C. I am trying to figure out how to add pictures of the old board. The new board documentation talks about jumper and resistor cuts for blower speeds. I did not cut anything. I along with the tech at ICM decided that was not the issue. I could not attach the documentation (to big of file).



ICM275


Description

Fan Control Center
Specifications

Input
Voltage: 18-30 VAC
Frequency: 50/60 Hz
Output
Contact Ratings:
20 amps @ 240 VAC on high
10 amps @ 240 VAC on low
Time Delays
ON: 60 seconds fixed
OFF: 60-240 seconds adjustable
Downloads
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Old 09-06-2009, 11:55 AM   #4
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Carrier 58SX Main Blower Turns On Without Command


typo fix The old board is a Carrier HH84AA015
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Old 09-06-2009, 11:55 AM   #5
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Carrier 58SX Main Blower Turns On Without Command


Is it grounded properly? If you look carefully one of the mounting lugs/grommets probably says ground beside it and needs a good clean connection with its screw to the plate and the plate needs good contact to the furnace. Try clean the edge connector also and see if any of the wires are pushed back out on the white plastic connector. FYI: Those furnaces are prone to cracked heat exchangers at that age.

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Last edited by yuri; 09-06-2009 at 11:59 AM.
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Old 09-06-2009, 12:08 PM   #6
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Carrier 58SX Main Blower Turns On Without Command


I took each contact (seven) out of the harness connector (to board edge connector), cleaned and reinstalled. Cleaned or inspected all vacuum and condensation lines. Cleaned the condesation trap and drain line all the way to the sump pump. The limit switch has been jumpered now for almost two hours without any fan turning on. NOTE: before the original Fan Relay board had problems I had condesation leakage from the A Coil. The drain was plugged and I cleaned and dryed out everything before the Air was turned on. It was 2-3 weeks later when I had the Fan Controller board relay issue.
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Old 09-06-2009, 12:16 PM   #7
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Carrier 58SX Main Blower Turns On Without Command


The limit control probably got water damaged and I would replace it anyway. It is a simple bi-metal snap disc and they can get old and fail. I would save some $$ for a new furnace as the secondary heat exchangers on those units are failing a lot. Get full of pinholes.
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Old 09-06-2009, 12:27 PM   #8
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Carrier 58SX Main Blower Turns On Without Command


If the fan does not come on in the next couple of hours I would say it is the Limit Switch. What I don't understand is that with fan off and after it turns on I was getting 26 Vac on both sides of the switch (closed) which is good. Could the switch intermittently open for a short period of time and trigger the new Fan Controller Board to turn the blower on. I did not have the O-scope set to trigger on anything. On "Otis", yes we miss all of them. When my son was born 17 years ago, I used to call him "Otis my boy." Then one day, he was about 8, we were watching Mayberry RFD and he witnessed Otis the town drunk. After that he did not like me calling him Otis. Now he understands the drunk Otis is also a classic character.
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Old 09-06-2009, 12:51 PM   #9
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Carrier 58SX Main Blower Turns On Without Command


A fluttering switch could do that, does it also have a resistor attached to the wire from it? That is a thermal cutout but it could be dying also. Intermittent problems are THE WORST but I kind of enjoy them on the internet but not when I am in the customers house. Just watched a anniversary special about how that movie was made with Jonh Landis interviews etc. Anything with the 2 Johns and Dan Akyroyd, Bill Murray Or Robin Williams is a classic for me.

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Old 09-06-2009, 02:05 PM   #10
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Carrier 58SX Main Blower Turns On Without Command


I do not see any resistor inline with the two red wires going to the limit switch. It has been almost 4 hours and no Blower Fan on. I will wait another 4 hours, and if no Blower Fan comes on. I will connect the thermostat back up. The thermostat is a 20 year old White Rodgers Setback...the way I see it, if its not broke dont fix it. If the blower never comes on in the next day with the thermostat connected I will order a Limit Switch. I will let the board know of the out come. Thank you all for all your inputs.
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Old 09-06-2009, 02:16 PM   #11
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Carrier 58SX Main Blower Turns On Without Command


If the switch is open you will get 24 volts across it. If closed Zero 0. Sounds like the switch is the problem.
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Old 09-07-2009, 03:32 PM   #12
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Carrier 58SX Main Blower Turns On Without Command


Furnace Blower was off for 10 hours with Limit Switch Jumpered and no stat connections. Reinstalled stat wires and no blower came on for approx. 2-3 hours. Then the blower came on for 60 seconds and shutoff for 120 second. This continued until I shut the main power off. Turned power back on and monitored signals. The stat is set for cooling and I noticed the "W" (heat) signal was at 24 Vdc. The "Y" signal was 0 volts. The temp was raised so the cooling was not working and I would of thought the "W" signal would be 0 volts and the "Y" signal would go to 24 volts only when the cooling kicked on. I disconnected the "W" stat wire from the Fan Controller board and so far the fan has not come on. This configuration has not been that long for I am looking at other signals and shut of power in some cases. Further montioring showed a 3-4 Vac signal on the MGV pin 1 signal on the Gas Valve. I disconnected Pilot Flame Switch and Pressure Switch which are part of this circuit and the 3-4 Vac siganl is still there. The only signal left is the board edge connector (7pins) pin 3 coming from the Old board time delay circuitry and the new board shows MC (microcontroller). I am starting think I might have multiple problems. The stat is now questionable with the "W" signal. Thanks for any input.
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Old 09-07-2009, 04:03 PM   #13
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Carrier 58SX Main Blower Turns On Without Command


OY!!
I would have to be there to see it. Not a lot of those older units left where I am. Lots of heat exchangers failures. Hvaclover and some of the other techs may remember it better, hang in there. Try a new thermostat as it looks bad. Don't get one with an automatic switchover from heat to cool function. The Honeywell Vision and Focus Pro models are good. Start a new post if you don't get any replies by tomorrow, not sure everyone follows all the threads.

Last edited by yuri; 09-07-2009 at 04:12 PM.
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Old 09-07-2009, 04:14 PM   #14
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Carrier 58SX Main Blower Turns On Without Command


Still no fan turning on. I plan on going to Johnstone Supply tomorrow and pickup new Limit Switch and Stat. I was hoping to get a similar White Rodgers Stat, for the original one I had lasted 20 years. What do you think about White Rodgers (did the quality change..china??). Is the Honeywell one you mentioned equivalent in your opinion?
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Old 09-07-2009, 05:03 PM   #15
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Carrier 58SX Main Blower Turns On Without Command


Actually I prefer White Rodgers, thats what I sell. Unavailable at HDepot here. Both are very good brands and comparable. If you are looking for a touch screen type the WR has a blue screen which is a bit easier to see in some conditions. The lower end models/$$ of both brands are nothing special. Those 20 yr old WR can do some weird things and it should be replaced. The connector pins/harness get oxidized/loose and that may be the problem (non cleanable). Non repairable and they are usually good for 15 yrs irregardless of brand.


Last edited by yuri; 09-07-2009 at 05:06 PM.
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