Furnace Issue - Open High Limit

[Mike_H]

All,

I have a Goodman furnace, about 15 years old. Heat stopped working for me this weekend. Backtrack a little, and I woke up one morning a couple weeks ago and the furnace fan was running, but not blowing heat. I shut it down, but forgot to read the number of blinks on the board. When I started it back up, it worked fine. Well, Silly me forgot to call a service Tech about it and the problem came back last Thursday. I shut it down, turned it back on and it worked again, until Friday evening.

I'm getting 4 blinks on the control board which means open high limit (high temp). I have two temp limit switched that I can find in that circuit, wired in series. I looked into the A/C evaporator looking for dust and dirt or anything else that might prevent airflow. That all looked good. Then I stuck my inspection camera into the main blower and looked at the secondary heat exchanger (its a high efficiency model). Little more dirt, but I can still see the fins and whatnot. I also put a new filter in, just because. I don't think its air flow related.

I've tested both the limit switches and they both show continuity. However, when my furnace tries to fire, the inductor blower turns on and almost immediately the main blower turns on and I get the fault. Under normal operation, the inductor blower turns on, then the burners kick and finally the main blower turns on. Its gotta be a bad switch, right? Maybe a bad connection? The burners don't even try to fire currently.

What am I missing?

 

[freedom_in_4low]

I have a Goodman furnace

found the problem


i kid, i kid. I have no idea whether there's anything wrong with Goodman, I just was programmed to hate them because they're a subsidiary of Daikin, which was a major competitor when I worked for Trane. (interestingly, I've had nothing but Rheem, Carrier and Goodman stuff in every house I've owned)

Heat stopped working for me this weekend. Backtrack a little, and I woke up one morning a couple weeks ago and the furnace fan was running, but not blowing heat. I shut it down, but forgot to read the number of blinks on the board. When I started it back up, it worked fine. Well, Silly me forgot to call a service Tech about it and the problem came back last Thursday. I shut it down, turned it back on and it worked again, until Friday evening.

I'm getting 4 blinks on the control board which means open high limit (high temp). I have two temp limit switched that I can find in that circuit, wired in series. I looked into the A/C evaporator looking for dust and dirt or anything else that might prevent airflow. That all looked good. Then I stuck my inspection camera into the main blower and looked at the secondary heat exchanger (its a high efficiency model). Little more dirt, but I can still see the fins and whatnot. I also put a new filter in, just because. I don't think its air flow related.

I've tested both the limit switches and they both show continuity. However, when my furnace tries to fire, the inductor blower turns on and almost immediately the main blower turns on and I get the fault. Under normal operation, the inductor blower turns on, then the burners kick and finally the main blower turns on. Its gotta be a bad switch, right? Maybe a bad connection? The burners don't even try to fire currently.

What am I missing?

is there a good way to check continuity of the entire circuit, with the switches in place? Other than that...I wonder if there's a broken trace or solder joint in the board itself?

I admittedly haven't had occasion to really get into residential equipment, but that's what I would do first.

 

[Mike_H]

found the problem


i kid, i kid. I have no idea whether there's anything wrong with Goodman, I just was programmed to hate them because they're a subsidiary of Daikin, which was a major competitor when I worked for Trane. (interestingly, I've had nothing but Rheem, Carrier and Goodman stuff in every house I've owned)



is there a good way to check continuity of the entire circuit, with the switches in place? Other than that...I wonder if there's a broken trace or solder joint in the board itself?

I admittedly haven't had occasion to really get into residential equipment, but that's what I would do first.

Yeah, I was thinking about tracing the circuit that way tonight...but wouldn't you know...the damn thing started working again! Hard to troubleshoot a problem when its not currently being a problem. The only difference between today and Saturday Evening when I threw in the towel is about 36 hours.

 

[Only TJ's]

in sequence, you should see, inducer motor, hot surface ignitor, gas valve, flame rectifier, then blower. sounds like your inducer is going, is your ignitor firing? it's been forever since i've looked at a goodman, but are the two limit switches you see by the burners? if so those are flame roll out switches and not the ones you're looking for. there should be one/maybe two up high on the firebox for a hi-limit

 

[Mike_H]

in sequence, you should see, inducer motor, hot surface ignitor, gas valve, flame rectifier, then blower. sounds like your inducer is going, is your ignitor firing? it's been forever since i've looked at a goodman, but are the two limit switches you see by the burners? if so those are flame roll out switches and not the ones you're looking for. there should be one/maybe two up high on the firebox for a hi-limit

No...I know the two for roll out. They are near the burner box. The main limit switch is in the middle of the unit, between the burner tubes and the secondary heat exchanger. The auxiliary limit switch (which is a manual reset) is below the secondary heat exchanger, where the main blower enters.

 

[Mike Z]

No...I know the two for roll out. They are near the burner box. The main limit switch is in the middle of the unit, between the burner tubes and the secondary heat exchanger. The auxiliary limit switch (which is a manual reset) is below the secondary heat exchanger, where the main blower enters.

Did you happen to check outside for any blockage in your air intake port?

 

[TNHEADDUCK]

Did you happen to check outside for any blockage in your air intake port?

Does it have a proving switch that is activated by the fan?

 

[Mike_H]

Did you happen to check outside for any blockage in your air intake port?

Yup, both clear

 

[Mike_H]

Does it have a proving switch that is activated by the fan?

Proving switch? Like a flapper that moves with the fan pressure?

 

[TNHEADDUCK]

Proving switch? Like a flapper that moves with the fan pressure?

Air flow switch, you could always jumper wire the switches/wires until you find the correct bad circuit. Then just ring out the wires.

 

[Mike_H]

I don't believe it has any type of air flow switches...it definitely has pressure switches though.

 

[dodj]

in sequence, you should see, inducer motor, hot surface ignitor, gas valve, flame rectifier, then blower.

This. ^^. What you describe is the blower coming on almost immediately... before ignition. Sequencing is controlled by the main board. However, if your high limit is tripped/bad it may be disabling the ignition and turning on the blower to move heat out of the appliance. I would jumper out the high limit temporarily then test ignition. Then you will have an idea if you have a switch or wiring or board issue. REMOVE THE JUMPER. I work on industrial furnaces bigger than your house, not house furnaces, so I may be missing something simple for you to check.

 

[TNHEADDUCK]

I don't believe it has any type of air flow switches...it definitely has pressure switches though.

Same thing just different terminology I guess, I worked on baking ovens in a commercial bakery that the gas system used several different types of safeties/switches. The jumper wire was my favorite tool when working on them.

 

[Mike_H]

Yeah, when it faults, I'll start bypassing safeties to figure it out. My dilemma is that I have a tech scheduled for today and the damn thing is working again. Do I keep the appt or cancel and "hope" that I can figure it out next time (cuz it will happen again).

 

[TNHEADDUCK]

It will be hard for him to fix if it aint broke, some techs will just throw parts at it till they get the right one. I would cancel.

 

[Mike_H]

The tech just left...I ended up buying a new furnace and A/C...which I was kinda expecting anyway. Couple things going on...One is the thing is just old and wasn't a great furnace to begin with. My A/C was decent, but it is 28 years old...so I guess now is the time. The second is that after my remodel, the furnace is kinda being starved for air. So they are going to fix that too and install another return on my lower level.

And holy crap, this stuff is expensive...

 

[freedom_in_4low]

holy crap, this stuff is expensive...

You can say that again. I suppressed that particular line item into my subconscious but I'm building a house and had to buy a 4 ton and a 3 ton heat pump with electric auxiliary, plus all the duct work and wiring for the install. I've always had gas but this place is out there and we'll have propane for cooking and hot water only. And since we have ice storms that knock power out for days at a time and 4 acres of post oak trees, I'm 5 figures into a fancy wood burning fireplace that should do a decent job at heating the entire house, so I consider that part of HVAC as well rather than the useless gas logs they like to use around here.

 

[sab]

And holy crap, this stuff is expensive...

And your tech probably informed you of the federal minimum SEER standard that changes Jan. 1 in order to get you to buy now (happened to me last month with a rent house). Buying a system made after that date will be even more expensive...

 

[Mike_H]

And your tech probably informed you of the federal minimum SEER standard that changes Jan. 1 in order to get you to buy now (happened to me last month with a rent house). Buying a system made after that date will be even more expensive...

He did let me know that, but he was a good dude and didn’t try pressuring me at all. I was asking if it made sense to do it now or later. Now made more sense

 

[Mike_H]

You can say that again. I suppressed that particular line item into my subconscious but I'm building a house and had to buy a 4 ton and a 3 ton heat pump with electric auxiliary, plus all the duct work and wiring for the install. I've always had gas but this place is out there and we'll have propane for cooking and hot water only. And since we have ice storms that knock power out for days at a time and 4 acres of post oak trees, I'm 5 figures into a fancy wood burning fireplace that should do a decent job at heating the entire house, so I consider that part of HVAC as well rather than the useless gas logs they like to use around here.

My folks had a geothermal heat pump and a outdoor wood burner. He used wood to heat water, the house, and his pole barn. It was a very nice system, aside from having to go load wood into the boiler 2x a day. Better than propane or pure electric, but the convenience of natural gas is hard to beat