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I have an American Air Furnance Model. The code reads

Hello Pearl, I have...

Hello Pearl, I have an American Air Furnance Model . The code reads pri***** *****mit switch is open. I replaced the limit switch with an original part and the code is still saying the primary high limit switch is open?

Contractor's Assistant: Did you double-check the thermostat's settings? And what about the filters?

The filter is replaced, the thermostat is new and set on 80 degrees.

Contractor's Assistant: Do you plan on doing the work yourself?

Can you advise?

Contractor's Assistant: Anything else we should know to help you best?

That’s everything....

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Customer reply replied 4 months ago
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Answered in 20 minutes by:
10/21/2017
BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22,921
Experience: Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Hello,

my name is Billy. There can be more than one limit and also different types.

And there is always a possibility of a bad circuit board. Do you know what and where the roll out switches are? Or can you post a pic of furnace and i can circle

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can you please post a pic of the burner area?

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Customer reply replied 4 months ago
Can you explain why you need the picture?

I was going to show you the other "limits" in the circuit. An open limit can be one of 3-4 switches

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Customer reply replied 4 months ago
Ok. I will go take the picture now!

standing by

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Customer reply replied 4 months ago
In route about 10 mind away.
Customer reply replied 4 months ago
Hello??? Are you there???

First follow all the wires I made red X's at HERE

Also click ...HERE

If the limit on wall is new

And pressing center of roll out button does not reset......AND the wires marked do NOT go to another limit switch...then the circuit board is bad.

But what happens is a wire leaves the circuit board with 24volts....stops and runs through a limit, runs to another etct etc then runs back to circuit board. It is this loop that we need to check...if everything in the loop is closed and 24v gets back to board then the board is bad.

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Customer reply replied 4 months ago
I replaced all the limit switches yet the control board is still saying pri***** *****mit circuit open. So, do we need to replace the control board? Where is the best place to order an original control board?

does the bypass include the one we couldnt get to?

Last test to see if board (seriously) :)

When you follow the wires for the limit circuit....they both end up at the plug on the board.

Can you identify these 2 wires as they leave the plug on the board?

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Customer reply replied 4 months ago
the wires go back to the control board. There is also, a rollout switch on the right interior side of the Furnance that has wires that tether back to the control board and the pri***** *****mit switch.
Customer reply replied 4 months ago
The two wires go to the limit switch from the control board.

ok just to confirm...the limit you replaced....the wires go direct back to board?

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and not through another limit?

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Customer reply replied 4 months ago
The switch on the left side is tethered to the pri***** *****mit switch inside the plenum, but there is one wire on the connector space of the primary switch that goes directly to the Control board.
Customer reply replied 4 months ago
Hi Billy, The wires are connected based on the original layout from the factory.

Thank you..

Then you will need to replace board...the rollout and limit circuit return on separate wires...so you have a bad board.

Like this one

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Customer reply replied 4 months ago
Hi Billy, Where is the best place to buy an original Control board for the American Air? I sent a picture of the control board. Also, why doesn't the Control Board has an diagnostic indicator Code of when the board is bad? Is there a way to test in the future without relying on the control board indicator light?

you start at the wire leaving board carrying 24v TO the limit...and if limit is closed the 24v returns to the board and verifies the limit is closed. When the board is bad it does not recognize the 24v being returned.

The only confirmation is to verify the 24v is getting back to the board...and if board codes open limit we know board is bad.

This board is older has no provision for a "bad board" diagnostic

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Customer reply replied 4 months ago
I got the new control board In, but am getting diagnostic code of Pressure Switch NC Circuit Open, yet there is a brand new pressure switch on the furnace that was added today. What is causing this?

Does the pressure switch wire run to any other device or just 2 wires from board direct to ps?

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Customer reply replied 4 months ago
There are three wires coming off of the new pressure switch. 1 red wire goes to the gas valve, 1 blue wire that connects to the wire harness that is connect to the control board and 1 purple wire that is connected to the same wire harness that is connected to the control board.

when you start furnace does the exhaust fan start?

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Customer reply replied 4 months ago
Hi Billy, The exhaust fan does not start.

When you turn the thermostat to heat...and the code is blinking for pressure switch...there is a black and white wire that go to the exhaust.....can you tell me if this black and white wire has 120v between them?..is the exhaust motor warm, hot, cold, humming etc?

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Customer reply replied 4 months ago
Hi Billy, The thermostat is hard wired jumpered. The exhaust motor is cold. From the blower motor, the white wire is connected to the new control board at the neutral terminal section and the black wire is connected to the EAC terminal section on the control board. Where do I place the voltmeter to check for the 24 volts?

Ok that black wire will not go to EAC...It goes to IND....Unless it is listed as something else on the new board

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Eac = electronic air cleaner (if equipped)

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Customer reply replied 4 months ago
What does IND mean? Is that for the inducer motor on the blower? Should I switch the wire the turn the power back on?

IND means means inducer motor which is the exhaust motor.

If you have a full pic of the new board I can direct...but EAC will not have 120v when we need it.

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Customer reply replied 4 months ago
Hi Billy, It’s firing up, but now I’m getting code 4, which says an “airflow control circulation problem”. Never had that issue before. Do we need to increase or add more cold air return ducts?

Is blower running and heating home?

The unit is operating ok but codes circulation?

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Customer reply replied 4 months ago
The Furnance has the only 6 “flex ducts” coming off the plenum to the heat registers which are 30 feet away from the furnance which is in the basement. There is only 1 cold air return. The furnance is an 80% efficiency with 45,000 btu’s

Ok,

You need the same sq inches in return as you have in supply.

I would actually cut a register in right off the top of furnace...dump the extra heat in basement or wherever the furnace is...It would be great to more return to furnace...easier said than done usually.

I am glad you have it fired up!

Just rate service (5 star system) to move off the active list

Billy

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Customer reply replied 4 months ago
I hear and see the fan turning as the heat builds up inside the plenum, but the furnance shuts off before the blower distributes the heat through the vent ducts. The furnance is behaving the same way before adding the pri***** *****mit switch, 2 new roll out switches and new control board. It’s only giving a new code for airflow now.

On the circuit board....what color blower motor wire is on HEAT terminal?

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ok right now it is the slowest blower speed for heat.

Is there a yellow or blue wire from motor that is terminal M1, M2 or PARK?

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Customer reply replied 4 months ago
I mean red wire on the HEAT terminal of the spade connector on the control board.

ok coming from the blower motor...there is black (which is on COOL)

Red (which is on HEAT)

White (on neutral)

Then we have 2 unused speeds...yellow and blue.

Very simply I want to swap the red wire and blue wire.

This will raise the blower speed.

Are you sure the blower that blows air out the registers is running after the burner is on for 40 seconds? The exhaust motor is attached to chimney pipe and main blower in bottom behind the panel

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Customer reply replied 4 months ago
I don’t see a yellow or blue wire from the blower motor terminal or anything with M1, M2 or Park.

dont the wires marked here run with the black and red ?

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Customer reply replied 4 months ago
It’s not blowing anything out after it runs for 40 seconds. The flames burn for 3 minutes then, the furnance shuts off before distributing heat into the vent ducts. I even opened to vent ducts off the plenum to check for airflow. No heat is being distributed. The furnance shuts off.

sounds like a major electrical hit....this means the motor or capacitor is bad.

see here

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you can, but it sounds like the motor has an issue or the capacitor...board is new...

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Customer reply replied 4 months ago
What is the best way to test the motor? Where is the capacitor located?

the capacitor is behind the panel in the lower section usually mounted on the blower housing.

remove panel and show me what you see

BillyHvac
BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22,921
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