Completely Stumped - Goodman "Open High Limit"

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Old 10-25-11, 12:26 PM
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Completely Stumped - Goodman "Open High Limit"

Hello -

Hoping someone out there has some advise, otherwise I am going to resort to calling a tech out at $150 / hr.

I live in lower MI and have a Goodman GDH80904bxac furnace. I am getting the blinking light error code meaining "open high limit", but here is exactly what is happening...

Furnace will run fine for anywhere from 10 minutes to an hour, then the burner will shut off, blower will continue to run and I will get the error code for "open high limit". I will then disconnect the power let it sit for a few hours, turn the power back on and same cycle starts again, it will work fine, then give me the error shortly after.

I have checked my primary and rollout limits and both are closed. I put a new furnace filter in a month ago, before turning it on for the winter. I have looked and nothing seems to be blocking my cold air nor my duct.

I consider myself a pretty handy guy and this is driving me crazy that I cannot figure anything out on this. Any suggestions are appreciated.
 
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Old 10-25-11, 03:14 PM
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It's very likely that the high limit switch is opening.


You need to test for that condition promptly after the burners shut off, and use an AC voltmeter connected to the sheet metal of the furnace and checking each side of the limit switch.

Also you can drill a small hole in the sheetmetal of the warm air plenum and insert a thermometer to measure the warm air temperature while the burners are operating. The limit switch probably has a high temperature on it that causes the limit switch to open.

Leave the thermostat set to a high temperature to keep the burner running continuously to see how high the temperature in the warm air plenum gets.
 
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Old 10-25-11, 05:03 PM
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Do you have an evaporator coil under this 80% downflow furnace?
A dirty evaporator coil can cause this.
 
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Old 10-25-11, 05:53 PM
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I have tested the primary limit right after and I have continuity. I will try the thermometer to see what my temp is. I believe the primary limit would kick at 180 degrees, does that sound about right?

Houston - I do have an evaporator coil, I will check that also

Thanks for the tips
 
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Old 10-25-11, 06:31 PM
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You said you replaced the air filter. If you used one of the "high performance" pleated filters, it could be the source of the problem. With marginal duct systems, I've seen it many times.
 
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Old 10-25-11, 08:47 PM
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Please describe your test of the limit switch in detail.

And don't guess about the limit switch temperature. Usually the temperature that it opens is listed on the exterior part of the switch.

"L180" would indicate a limit switch that opens at 180 degrees for example.
 
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Old 10-26-11, 05:51 PM
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In testing the limit switch I have disconnected the wires from it and put a lead from the meter on each tab of the switch.

I haven't drilled a hole in the side yet, but checked all 3 limits again today as well as cleaned the evaporator coil and tried running the furnace just without the filter
 
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Old 10-26-11, 05:57 PM
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Drill the hole & check the temp. This will likely tell us if the limit is weak or if it is really seeing the kind of temperatures which would cause a properly operating switch to open.
 
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Old 10-26-11, 08:50 PM
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Your test of the limit switch is no good.

You need to connect one test lead to the C terminal on the circuit board and use the other to test the two connections to the limit switch when the furnace shuts off and the diagnostic code turns on.

Turn the thermostat way up so the furnace will run continuously to see if it will limit out.

When the burners shut off, you should still have 24 VAC to one side of the limit switch and 0 volts to the other side. That indicates that the limit switch is open.


A repairman would have completed this test about five minutes after arriving. Unfortunately, you really don't have a clue about what's happening or how to do things.

And you don't follow directions. When you are asked for a detailed description of what you have done the result is a vague description.

You need to provide detailed descriptions of what you do and what you observe or frankly, it's a waste of time.
 
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Old 10-27-11, 07:22 AM
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i think Its the limit that sits above the burners. Replace it. It seems logical. High temp is reached, burners shut off. fan runs to cool off the heat exchangers, then it should come back on automatically. It is not a good idea to turn the furnace off atfter the temp limit is reached. let the fan run and cool it off first.
 
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Old 10-27-11, 02:31 PM
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Seattle are you saying that a meter would show continuity on the switch if it was open? Pretty sure I have a decent idea of what I am doing, but I called a tech out today from the place that installed the furnace. He said all the limits are fine and there is nothing wrong with them. They are all closed when the error is reported. He didn't know what else to do besides replace the board.
 
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Old 10-27-11, 02:35 PM
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That's a fairly common problem with Goodman boards but before condeming it I wanted to be sure. For some reason, they will give a false "high limit open" code when the problem is actually with the board.
 
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Old 10-29-11, 06:50 AM
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the FAN limit closes on temp rise ...for fan ON either 115V speed wire or 24Vs of a fan relay the HI-LIMIT opens on temp rise 24V control knocking the burner off...and let the fan take the heat off the burner cause the heat might be keeping the hi limit open on a repower....the HI LIMIT might be fatigued so it is slowly reacting to fast just above the FAN ON closure around 160F give or take a degree HI limit is 180F or above.if the coil,filter and you have a solid return air thru the grill from the space i would go with a weak HI LIMIT...if you need heat gots to do what you have to do there till you replace it....if you do run the heat get back on what the discharge air temp is going thru the A coil area...if its 160-170 and the HI is open thats the proof....
 

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Old 10-29-11, 07:55 AM
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Sminker,
I know of NO furnace which would have a switch to bring the fan on at, or even near 160[SUP]0[/SUP]. 140 would be high on today's furnaces.
 
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Old 10-29-11, 12:56 PM
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I replaced the board yesterday and everything has been working fine. Hard to believe the board was bad on a 3 year old furnace
 
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Old 10-29-11, 01:31 PM
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The part may well be covered under a guarantee with the manufacturer. Check your owner's manual which usually contains the guarantee.
 
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