I have a Carrier 58SSB080 with a label that says it was made in 1985. Last year, the bathroom above the furnace flooded and dripped all over the furnace, shorting out the circuit board in the blower compartment and apparently also the gas valve. I replaced the board and valve and thought everything was OK again but I wasn't really paying a lot of attention to how it was working. The draft motor was very noisy, so I replaced that and the draft blower wheel as well and everything seemed to be working fine. This year, I noticed that when the thermostat commands the heat on, the draft motor starts and the burner and blower both run normally, but only for a few minutes. It doesn't run long enough to bring the house up to the thermostat temperature. I changed out the thermostat with a different model and it still does the same thing. A few seconds after it shuts down, it will start right back up again and goes through the normal cycle except it shuts down early again. The thermostat says the furnace should be running constantly, but it doesn't. It may take 45 minutes to bring the house from 62 degrees to 71. Something is not right about the way this is working, but I don't understand where I should look for the problem. Could this be a high limit thing or a draft safety switch thing? Before the control board was replaced, I noticed that the pilot igniter ran constantly, even after the pilot and burner were lit. That behavior did not change after swapping out all those parts, but that doesn't seem right to me either. Could these be related? Any ideas or insights are greatly appreciated... :)

John Rizzo

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General/Is my furnace overheating?

https://www.askmehelpdesk.com/heatin...tml#post268203

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Originally Posted by NorthernHeat

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general/Is my furnace overheating?

https://www.askmehelpdesk.com/heatin...tml#post268203

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Thank you for the fast answer! As far as checking these items, can you tell me if there is a way to determine if the "main limit open" condition is present? I am going to remove the filter and leave the filter cover off so plenty of air can get through to the blower compartment. Have you ever heard of issues where the blower wheel gets dirty and doesn't move air as efficiently? This furnace is 21 years old and I can only vouch for its maintenance history for the past year and a half. It may have been abused or not maintained before that.

I know that the previous owners of this house were a bunch of looney-tunes morons based on some of the absolutely stupid things they did to screw up the mechanicals of this house. One of their boneheaded moves was to completely close off one of the cold air returns. They decided a doorway needed to be bigger, so they installed the flooring right over the top of the cold air return. The other 3 returns are flowing fine and the furthest one doesn't have much suction, so I have always assumed there was still sufficient flow with one return covered. Is there a way to measure this? Can I measure the blower amperage to figure out if it's working too hard? Should I just call the local HVAC shop and have them do the pressure tests? What I'm trying to eliminate here is whether the airflow could be a problem or perhaps the limit switch was damaged when I had that water problem last year.

Thank you so much for your help. I appreciate your attention. I don't see on the page where I can rate your assistance. Am I missing something?

John
:)

Wow that was allot of questions. Yes to moist of them :-)
Simply put do a temperature rise

Rise=Tr
Supply temp'=St
Return air temp'=Rt

Tr=St-Rt

Around the nomanclature plate (model/serial number plate)
It should state what the temperature rise should be.

Yes, a blower wheel can be to dirty,in which case the evaporator coil probably is too.

Quote:

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Originally Posted by NorthernHeat

Wow that was allot of questions. Yes to moist of them :-)
Simply put do a temperature rise

Rise=Tr
Supply temp'=St
Return air temp'=Rt

Tr=St-Rt

Around the nomanclature plate (model/serial number plate)
It should state what the temperature rise should be.

Yes, a blower wheel can be to dirty,in which case the evaporator coil probably is too.

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You were right on. I let more air into the cold air return system and now the furnace runs non stop until the thermostat shuts it down. It must be a high limit issue. The lack of one cold air register is probably the source of the problem. I am going to remove the blower and give it a good vacuum and oil the motor and figure out some way to move that cold air duct to another wall. The coil is hard to access. I have to cut a hole in the drywall of the stairwell to get access to the ducting around it, so that is going to have to wait until spring when I can shut the system down for a while and not freeze to death. I'll get it done before summer cooling season and hopefully keep the bills down. They raised our electric rates 24% at the beginning of the year, so it's going to be a record year for electric bills. Better make sure I'm getting my money's worth, eh? :) After all the time and money I've put into this furnace, it better last a while longer. It's almost 22 years old, so the heat exchanger will probably crack or corrode as my next crisis.

Thanks very much for all your help. I really appreciate it. I just used the "Support this Member" link to express my gratitude and hope others will do the same.

John