American Standard freedom 80 furnace
#1
11-14-15, 09:27 PM
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American Standard freedom 80 furnace
I'm needing some help with my HVAC unit. Last winter the unit gave a four blink code that means open limit device. After talking to a friend that's a tech he told me to take out open limit device and tap it lightly on a flat surface. This fixed the issue. Flash forward to present.Well it got down to 20 degrees last night and I turned on my unit, bliwing cold air I went into the attic to check unit. Same open limit 4 blink code. I tried the tap trick again but no luck. I checked continuity on limit switch with no luck. Another trick I was told to place a jumper between these two wires and this should close the switch, tried this but as soon as I called for heat again I got the 4 blink code, I'm not getting hot air because burners are not coming on, I assume this because of open limit device blink code, and as I watch unit burners never fire. Any other troubleshooting tips would be appreciated. Thanks for the help in advance
#2
11-14-15, 10:34 PM
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Welcome to the forums.
There are usually two high limit switches. One can be behind the blower and hard to see. Follow the yellow safety stat wiring.
You have a problem with the furnace plenum overheating. Dirty filter, dirty blower wheel, too many closed registers, blower fan running slow, blocked return vent, insulation blocking blower squirrel cage are all problems that can cause this problem to occur. Now you may need to replace the sensors if they aren't resetting properly.
The "bang them down on the table" stunt is only a temporary solution to an ongoing problem.
There are usually two high limit switches. One can be behind the blower and hard to see. Follow the yellow safety stat wiring.
You have a problem with the furnace plenum overheating. Dirty filter, dirty blower wheel, too many closed registers, blower fan running slow, blocked return vent, insulation blocking blower squirrel cage are all problems that can cause this problem to occur. Now you may need to replace the sensors if they aren't resetting properly.
The "bang them down on the table" stunt is only a temporary solution to an ongoing problem.
#3
11-15-15, 12:24 PM
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I have replaced filter, I have no closed registers and my squirrel cage is relatively clean. If you use a jumper in the place of these limit switches shouldn't they allow them to come on
#4
11-15-15, 05:53 PM
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Yes.... you can jumper around the sensors for testing. There is one that is hard to jumper as it's not easily seen.
Post the complete model number for you furnace so I can look at the wiring diagram.
The wiring diagram is usually on the blower door and you can also see all the safeties listed there.
Post the complete model number for you furnace so I can look at the wiring diagram.
The wiring diagram is usually on the blower door and you can also see all the safeties listed there.
#5
11-16-15, 04:01 PM
Banned. Rule And/Or Policy Violation
The primary high temperature limit switch resets automatically. IF there is a secondary limit, it is usually manual reset.
You need to identify which limit is remaining open, since they perform different functions.
You will need to use an AC voltmeter to see whether it is the primary or secondary limit switch which is failing to close and allow 24 VAC to pass from the switch input to the switch output connection.
You need to identify which limit is remaining open, since they perform different functions.
You will need to use an AC voltmeter to see whether it is the primary or secondary limit switch which is failing to close and allow 24 VAC to pass from the switch input to the switch output connection.
#6
11-17-15, 05:36 PM
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As far as model number I can find a specific one, it has a list of about 15 different model numbers next to inside panel wiring diagram
#7
11-17-15, 05:53 PM
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There are 2 sleeved groups of wires: one with an ivory-ish/white wire and a red wire, and one with white, red, yellow and green wires. The blue wires you see were never used.
Thoughts on the correct wire order?