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miscrap 09-11-2013 01:26 AM

Something keeps running on A/C
I had a new Carrier furnace & A/C installed in June of 2004. The model # on the furnace is 58CTA090-14. I returned home from a fishing trip today to temps of 95 degrees. (My wife and teenage son were home while I was gone.) When I walked in the house felt a little warm and clammy. I checked the thermostat, it was set at 77 but the temperature in the house was 79. When I looked at the furnace I noticed that I didn't see the filter in the slot. I took off the return that's in line with the filter and noticed that the filter was partially sucked into the fan, although the fan was able to run. When I pulled the filter out it was wet, but came out all in one piece. There was a little water on the floor around the furnace. I found out that my son had tried to do a good deed while I was gone, and had replaced the filter for me, but he had put it in backwards, with the air flow arrow pointing in the wrong direction. I replaced the filter, and the temperature in the house came down to 77 in a short time. The mugginess also was removed. However, I noticed that when the outside condenser and fan shut off I could still hear something running. I removed the cover on the furnace and saw what looks like a clock spring (have no idea what it really is or what it's for) continuing to spin. I don't recall hearing this running before. Is this normal, or do I have a problem? I noticed a round glass window on the front of the furnace, and I see an amber/yellow light flashing. There are 2 short flashes, then 1 longer flash. A pause, then it repeats. Any help would be appreciated. Thanks.

yuri 09-11-2013 09:11 AM

that clock spring thingy is the cooling fan for the ventor motor/fan and it can spin on some days from draft thru the chimney causing air to move thru it. not a problem.

check the codes on the back of one of the doors to see what it is.

miscrap 09-11-2013 09:47 AM

Thanks for the reply, Yuri. Unfortunately, there's no wind, and the fan is being powered - I can't stop it with my finger.

beenthere 09-11-2013 11:43 AM

The control board may have gotten wet. And the relay for the inducer may have shorted out.

Remove the wire from the W terminal.

yuri 09-11-2013 11:58 AM

Beenthere is correct. I found a 58MTA manual very close to yours and code 21 is gas heat lockout. Looks like water got on the board and damaged it from the AC coil freezing up from lack of air flow. Going to need a new board by the looks of things. Check the code on yours but I am 99.99% sure it is the same as the MTA. may have a retrofit board/kit now and it can be very tricky to install unless you have done some electrical work. has a tricky fragile 16 pin flat edge connector that can be put on backwards and damaged if you are not skilled or careful. is a good site

miscrap 09-11-2013 09:33 PM

New board ordered, will be here tomorrow. Thanks for the help! I'll post the results (or questions if I run into problems). Thanks for the help!

yuri 09-12-2013 10:18 AM

Yur welcome.:)

miscrap 09-12-2013 04:04 PM

Picked up the board (turned out the place I bought it from was 5 minutes from my house). Replacement looks pretty straighforward - shut off power to furnace at circuit breaker, remove wires from old board, install on new board (one at a time so as not to get mixed up), install board, flip on power. I've done a bunch of internal computer work, this looks pretty similar. I'm going to take a closeup picture of the old board before I start, just as a backup view just in case. Any cautions I should be aware of?

yuri 09-12-2013 04:37 PM

Is the board EXACTLY the same as the old one or is it a kit with a bunch of wire harnesses/retrofit kit? If it is not the retrofit kit then the swap is easy. If it is the kit then you need to CAREFULLY and EXACTLY follow the pics /harnesses they give you and make sure the skinny flat 16 pin connector has the proper orientation and you install it correctly w/o damaging any pins. not easy to remove once on as it has lock clips. I use a magnifying glass and if you look carefully on the board and connector there are very small matching numbers for orientation. make sure you hold the metal side of the furnace to ground yourself when removing the board from the bag so no static damages it.

miscrap 09-12-2013 05:01 PM

Thanks, Yuri! The board I picked up is identical to the old one. Got it for well under 1/3 the cost of the site recommended here. Brand new, still sealed in static bag, from a HVAC shop 5 minutes from my house. Planning on using an anti-static wrist strap like I do when I work on computers.

yuri 09-12-2013 05:09 PM

Good 4 U. I have no idea of the net markups but if they have the right part and new then that is great. The older units have a retrofit kit as the board style changed. Yours is newer so U got the new board.

Don't feel 2 bad Junior caused it as the average life of those boards is 10 yrs anyway. Had one customer stick a 3M filter in w/o removing the 1/2 of it wrapped in the factory plastic bag. Sheet happens.:laughing::yes:

miscrap 09-17-2013 01:07 PM

HEEELLLLPPPPPPP!!!!! New board put in, exact duplicate of original. Wires replaced one by one so as not to put in wrong place. Anti-static wrist strap used to avoid static electricity when handling board. Put the cover back on, turned on the circuit breaker, and the inducer fan is no longer running, BUT THE FURNACE FAN IS RUNNING! The thermostat is OFF!! Fan switch on thermostat is on AUTO. There are NO LEDs flashing. Please help!!! Supposed to warm up the next few days and will need the a/c - but can't have the fan running full time.

firedawgsatx 09-17-2013 02:25 PM

Did you ever reset the limit switch? It probably tripped and caused your fan to run when the air filter issue restricted the air flow. Try to reset that limit switch and see if that solves your problem.

On a lot of modern furnaces if the furnace sees a limit, it will bring on the blower and inducer fan in an attempt to cool everything off. I have seen this happen a few times in the cooling season on some furnaces located in an attic. It can get hot enough in the attic to cause some limits to open. The times I have seen this happen were usually when the homeowners were away on vacation and did not leaving the a/c on. They arrive home to find the blower running. I don't know where you furnace is located, but if it is in a HOT attic it might be something to think about.

If a temperature limit opens on modern furnaces, the logic says "the furnace is too hot!" and runs the fan (and typically the inducer) in an attempt to cool off the furnace. A limit switch that opens normally indicates that something is interfering with that stream of air.
The most common causes of that are a clogged furnace filter or a return air grille that is covered/blocked off.

miscrap 09-17-2013 02:36 PM


Originally Posted by firedawgsatx (Post 1242875)
Did you ever reset the limit switch? It probably tripped and caused your fan to run when the air filter issue restricted the air flow. Try to reset that limit switch and see if that solves your problem.

As I was working on it, I noticed a label on the front of the cover that says that a code 21 is Gas Heating Lockout. It also says "Control will NOT auto reset". Is this what you're referring to? How and where do I reset it?

Just thinking... when I replaced the air filter, the a/c ran normally, blower fan going on and off as necessary. The only problem was the inducer fan running. Now, after replacing the circuit board, the blower fan runs continuously, even though the thermostat is off and not calling for cooling or heat.

firedawgsatx 09-17-2013 02:51 PM

What I suggest is that you turn the power off to the furnace, set the thermostat to OFF and then turn the power back on to the furnace. Code 21 indicates the main gas valve relay (MGVR) or 2-stage furnace control is stuck closed or there is a miswire or short to gas valve wiring. Try the suggested step and let us know if the furnace controls reset and operates normally.

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