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Old 04-06-2012, 12:33 PM   #1
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Furnace not working


Got no heat. Air conditioning works.

Carrier natural gas furnace, Model 58PAV090-14 installed in fall of 2000.

The red LED on the circuit board is flashing fast and continuous whenever power to furnace is on. It is not providing any codes. Normal state of LED is on steady. Error codes on furnace say fast flashing light means 115V polarity reversed. (Not sure what that means with alternating current) Otherwise it references a twin furnace setup. I only have one furnace. One online post I found linked the fast flashing to a bad ground. I went through the circuit from the ground connection on the furnace case back to the service panel. (It's a 16 ft straight run down an open joist with one junction box making the wiring easy to get at.)

Thermostat replaced last fall**. If power turned on with Heat ON, main blower runs for 90 sec (which is supposed to be normal) then nothing but blinking light. Otherwise, turning on power does nothing but blink the light after a few seconds. I can hear relays in thermostat working and again, the AC works, so I don't think it's the thermostat.

I am assuming that the codes should show obvious things like igniter failure. The draft blower never turns on so it can't be sensing vent issues.

Anybody have any suggestions? Besides shoveling more money at the contractor.

**In a fit of helplessness because I was between road trips, I called the furnace installer when the thermostat went out. Paid $370 for a $40 thermostat. Then they wonder why my first reaction to HVAC problems isn't to call them. Through next week, temperatures will be in the 60's so it will be a bit cool. May have to cook some Easter turkeys. But I've got some time to futz with this thing.

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Old 04-06-2012, 08:02 PM   #2
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Furnace not working


mwpiper,

Turn off the power to the furnace. Open the furnace's compartment. On the circuit board there should be 24v terminals. R C G Y W. Disconnect all the t-stat wires from tha terminals (make sure you mark it down so you reconnect them). Get a Jumper cable or any electrical wires and connect R W together. Close the furnace compartment and power on the unit. If the unit works, then there is a problem with the thermostat or the wires. If it doesn't, then there is a problem with your inducer draft motor, which is the exhaust motor. If you want to be sure, then get a meter and test for a 120v while the heater is on. If you get 120v and the induce draft motor is not spinning, then it the motor for sure.


Last edited by Mr.HVAC; 04-06-2012 at 08:07 PM.
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Old 04-06-2012, 08:18 PM   #3
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Furnace not working


Got..to...get...to....pc....
90 second blower on means board recognizes power was off to board. After that it should start call. Do not touch stat once turned to heat. Let it blower on and then watch for codes.
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Old 04-06-2012, 08:21 PM   #4
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Furnace not working


If flashing fast means normal operation on heat yet nothing is happening than board is bad.
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Old 04-06-2012, 08:46 PM   #5
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Doc Holliday,

Not trying to slam you or anything, but according to his post. He said the blower turns on for 90 seconds which normal (Probably a carrier or bryant furnace), but after that nothing will come on. After the 90 seconds, The induce draft motor should starts. All of this is telling me that he has a bad induce draft motor. Since A/C works, I highly doubt that it is the board. Althought I could be wrong, unless he has a meter to test it out. sorry, but i dont want to see the guy replace parts after parts.

Last edited by Mr.HVAC; 04-06-2012 at 09:00 PM.
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Old 04-06-2012, 10:48 PM   #6
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Furnace not working


Thanks for the feedback. Cycled power with multimeter attached to inducer fan motor leads. It never varied from a 4 mv reading. Main blower ran for 90 seconds (timed it) then it turned off and nothing. On a hunch, I checked the ignitor for continuity. It read 88.4 ohms.
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Old 04-06-2012, 10:50 PM   #7
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Furnace not working


PS: Is there a relay on the board that feeds the inducer motor? If it goes bad, is it replaceable?
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Old 04-06-2012, 11:00 PM   #8
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Quote:
Originally Posted by Mr.HVAC View Post
Doc Holliday,

Not trying to slam you or anything, but according to his post. He said the blower turns on for 90 seconds which normal (Probably a carrier or bryant furnace), but after that nothing will come on. After the 90 seconds, The induce draft motor should starts. All of this is telling me that he has a bad induce draft motor. Since A/C works, I highly doubt that it is the board. Althought I could be wrong, unless he has a meter to test it out. sorry, but i dont want to see the guy replace parts after parts.
Its all good. Im not payinf attention to each post.
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Old 04-06-2012, 11:09 PM   #9
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Furnace not working


He can hook 120 straight to inducer to see if it comes on, or chek board voltage to inducer to see if its being told to come on.
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Old 04-07-2012, 11:31 AM   #10
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Furnace not working


mwpiper,

Don't worry about the ignitor, Just worry about the board and the induce draft motor. It's the sequence of the furnace. Since you have a meter, it will make things easier. Follow my steps,

Turn your meter to read voltage, attach the leads to the White and Black wires on the induce draft motor. Turn on the furnace to heat, and then watch the meter to see if you have 120v going into the induce draft motor. If you do, and the motor is not spinning, then you have a bad induce motor. If you dont, then the relay for the induce draft motor is bad. Since your furnace is a newer furnace, the relays are built inside the board, If that is the case, try to tap the circuit board. Sometimes the relays get stuck. Post back with results, or better film it for us.

To know if you have a good ground or not, follow this steps
On the 24v terminals R C W G Y (or something in that order). Turn your meter to read resistance (ohms). while the heater is on, put one lead into the C terminal, and the other lead into any metal on your furnace. You should get low resistance, .5 or less. If you have .5 or less, that means your ground is good. If you read anything more than that, then you have a ground problem.

NOTE: PLEASE BECAREFUL WHEN DOING THIS STEPS!!!! IF YOU ARE NOT COMFORTABLE, PLEASE CALL A HVAC TECH. I AM NOT RESPONSIBLE FOR YOUR ACTION. THANKS

Last edited by Mr.HVAC; 04-07-2012 at 11:38 AM.
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Old 04-07-2012, 11:44 AM   #11
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Furnace not working


Quote:
Originally Posted by mwpiper View Post
Thanks for the feedback. Cycled power with multimeter attached to inducer fan motor leads. It never varied from a 4 mv reading. Main blower ran for 90 seconds (timed it) then it turned off and nothing. On a hunch, I checked the ignitor for continuity. It read 88.4 ohms.
During the 90 seconds, it will not send 120v to the induce draft motor. After the 90 seconds, then the relay in the board will switch and then send 120v. Make sure that it touches the leads on the induce motor. When you said continuity, you mean resistance, ohms= resistance. 88 ohms is fine, it should ignites, depending what type of furnace you have, you might want to consider replacing that ignitor in the future.

Last edited by Mr.HVAC; 04-07-2012 at 11:47 AM.
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Old 04-07-2012, 04:22 PM   #12
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Furnace not working


If your inducer motor was being powered, not running and therefore the pressure switch was not closing, then the board should be giving a pressure switch led code.
Same with the igniter...different code.

Some folks here have reported some success with switching the transformer leads when faced with a led polarity code. Only attempt this with the furnace power off.

The ground check is a good idea for the way that a bad ground can cause erratic board behaviour.

If you have a thermostat that turns on the furnace by closing the (R & W) circuit (like 98% of all thermostats) then...
Turning off the power/ disconnecting the stat wires from the furnace/ jumpering R & W/ & turning the furnace power back on is the way of testing if the stat or that circuit is the source of the problem.

If nothing changes with these tests, then a board swap is next.

Last edited by how; 04-07-2012 at 04:28 PM.
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Old 04-07-2012, 05:14 PM   #13
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Furnace not working


To rephrase what I did earlier. I pulled the spade terminal back partially on the induce motor. It was still connected but exposed the bare metal of the terminal. I measured the voltage at those points with the motor still connected. It did not read above 4 millivolts. i.e. No power was supplied to the induce motor at any point. Just to eliminate the induce motor as a problem, if I make up an extension cord with spade terminals, I can connect the extension cord to the motor, plug it in, and the motor should work.

Quote:
Some folks here have reported some success with switching the transformer leads when faced with a led polarity code.
Was this done during initial setup or after the furnace had run for some time as mine has? The code legend for a rapid flashing light does say something about polarity, which is confusing since they're referencing alternating current. But it's a cheap test. I can try it. I'll try tapping the relays, too.

The weather is holding up and we are getting ready for family coming over for Easter, so I may not get to these tests immediately.

Are furnace control boards available retail? Are there magic incantations or programming involved in installing them, or should they be form, fit, function replacements?
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Old 04-07-2012, 06:42 PM   #14
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Furnace not working


mwpiper,

Is your ground good? try switching the wires on the transformer, if that doesn't work, then switch the wires from the junction box, the junction box is where the electric cord is wire nut with the furnace. both of that doesn't work, then I am afraid your board is bad, try tapping on the board before you replace it. Reserve polarity means that your 120v Neutral and Hot were wired reserve.
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Old 04-10-2012, 05:59 PM   #15
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Furnace not working


<sigh> No joy with the last batch of tests. Ground good. ALRO wired it up correctly. Reversing polarity of xformer changed nothing. Tapping board and relays did not free anything up.

I noticed that on the bottom half of the board, there is a green powder around the leads of the discrete components. It looks like copper oxide, but the upper portion of the board doesn't have it. Not sure what that would mean.

So...replace the board? I haven't changed a furnace control board in 28 years** I've found the board model number (1012-940-J) online for around $200 and includes specific reference for replacing my HK42FZ009 model. Problem is the picture is not the board I have in the furnace, which is 12 years old. Is this going to require rigging up a custom installation and finding comparable attach points for all the wires or is it just going to be the same thing rearranged but still basically compatible form and fit?

** I was a field service tech for a company that made induction furnaces, mostly for melting metal. Sized range from 15kW to 2MW holding up to 150 tons of molten iron. Foundry air and electronics didn't play well together so I always had spare board in my kit. Would kind of like to have a spare one now.

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