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I have a Tempstar model T9MVX080J20A1. Neither the furnace,

Customer Question
I have a Tempstar...

I have a Tempstar model T9MVX080J20A1. Neither the furnace, the fan, nor the air conditioner will turn on. I have checked the fuse and the door switch, both are good. I have no electricity to my thermostat. I do have power at the door switch (forgot I turned the power back on and got a buzz). I have visually inspected the control board and see no obvious signs that it is burnt. I have searched for a condensate switch, but don't see it anywhere if there is one.

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

Yes. Both are good.

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

Depends what the problem is.

Submitted: 11 months ago.Category: HVAC
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9/17/2017
HVAC Technician: airheatman, HVAC Technician replied 11 months ago
airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 9,369
Experience: Furnace, A/C and heat pump specialist.
Verified

Do you have 24 volts from transformer into furnace board and then 24v out of board at R and C where wires from thermostat connect o board?

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Customer reply replied 11 months ago
I will go check.
Customer reply replied 11 months ago
No power at R and C. The transformer is the little box beside the control board?
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Looks like stacked plates with a coil. If you can attach a photo with door panel remove I will point it out and the wires coming from trans to board will be marked 24v and com or similar

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HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Yep that is him. You will need door switch held in or taped in to test as it kills power to furnace. With door switch in, set meter to lowest ac Voltage setting above 24 (Usually 200) and check board where that blue and red wire connect to board.One lead on each terminal.

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Customer reply replied 11 months ago
I get no reading.
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Next set meter to lowest setting above 120 and do same where the shite and black wires to transformer connect.

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Customer reply replied 11 months ago
When testing the black and white wires, I got a small spark while attempting to get my probe behind the black connection. My other probe wasn't touching anything at the time.
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Hmm. make sure the black is not touching anything else,WE should not get a spark

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Customer reply replied 11 months ago
It's in a tight space and my probe may have touched the board and the terminal together. I will disconnect and try while it is not attached to the control board.
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

OK the terminal on board is where you will want to test, not the disconnected wire.

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Customer reply replied 11 months ago
Ok. I was trying to test the wires
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Those are power TO transformer FROM board. The red and blue low voltage are from transformer back to board.

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Customer reply replied 11 months ago
It reads 123.6
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

OK if 123 in on black and white but no 24v out on blue and red the transformer is bad and will need to be replaced.

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Customer reply replied 11 months ago
Ok thanks. ***** buy a transformer, will it have the 4 wires attached and coming out? If not I will likely have a service tech do it.
Customer reply replied 11 months ago
Sorry, just reading back, that last positive test was going red to black to white. Will re-test
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

If you buy a standard 120 volt/24 volt 40 va transformer it will wire exactly same and be labeled which wires are 120 and which are 24.

Now one thing to note is that something caused the transformer to bun up.You may have a short in the 24 volt wiring somewhere .

If you have a short somewhere you will blow another transformer if short is not repaired. I suggest wiring an inline fuse into the low voltage circuit in case there is a short.Then you would blow a 50 cent fuse rather than burning up another transformer if there is a short.

http://www.ebay.com/itm/5-amp-mini-Blade-In-Line-Fuse-Holder-Fuseholder-5AMP-Car-van-bike-boat-/270891779320

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Customer reply replied 11 months ago
still 124 v going black to white
Customer reply replied 11 months ago
Will it matter if the inline fuse is on the blue wire or the red wire?
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Not at al If there is a short it will blow the 30 cent fuse rather than new transformer.Take a visual at all wiring that could be nicked or chewed between units.Often exposed wire at outdoor will get chewed, hit by weed eater or crack due to sun.

If you have further questions, please let me know.

Thanks for letting me work with you.If my answer has been polite, professional,and thorough, please click one of the ratings before you go. If you still need help let me know!.Expert is not paid for assisting you until you rate answer.Feel free to follow up for 30 days at no additional cost. Bonus always appreciated if you feel justified.

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Customer reply replied 11 months ago
I will likely have to wait until Monday to buy the transformer, my HVAC shop is closed today. I will follow up once I get it in.I thank you for your time, if this solves my problem, then I will be very happy. You've been great!
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Look forward to follow up.Thanks for letting me help

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Customer reply replied 11 months ago
Sorry, one last question today lol. Is there a good way to trace where the short my be, other than simply visually looking for an exposed wire? The likely culprit is our new puppy that keeps digging behind the AC unit. I just don't see any exposed wires.
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Finding a short can be difficult. Easiest way to find is by process of elimination.If you can get several fuses, we can try different things until we no longer blow fuse to locate the short.

1.Disconnect all thermostat and outdoor unit control wires from the terminals on indoor unit control board.Turn power on to furnace and see if fuse blows.If it blows, the control board in unit is shorted and will need to be replaced.If not move to step 2.

2.Next I want you to connect those wires back one wire at a time turning power off and on to furnace after each one to see when fuse blows. Reconnect in this order

R G W Y and then C If you have C.(door switch has to be held in each time in order to have power to furnace.)

3. Go to outdoor unit. Disconnect the 2 control wires going to Y and C where they first enter the unit. Turn thermostat to call for ac. If fuse still blows we have a short in those wires between indoor and outdoor units.Could be chewed or skinned, possibly nicked by weed eater, etc. allowing wires to touch and create short.If it does not blow,we know short is inside of the outdoor unit.Move to next step.

4. Reconnect those 2 wires .Then locate the contactor relay in outdoor unit. Remove the small control wires on the contactor coil.Turn on AC.If fuse does not blow, the contactor coil is shorted and contactor will need to be replaced.If fuse still blows we know short is between where wires enter unit and the contactor.Move to next step.

5.Reconnect the contactor wires.Follow the control wires from where they enter unit and see what component may be in that circuit .(Pressure switches, time delay, defrost control board, etc).Follow same procedure of disconnecting wires to each of those controls and see if we find one that seems to cause fuse to blow when in circuit.Also look for any place the small control wires may be touch a hot gas copper line in unit that may have melted sheathing on wire and be allowing copper to ground to pipe.

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Customer reply replied 11 months ago
Is it just the blade fuse on the control board I will be watching? And is this something I need to replace the transformer first to find?
HVAC Technician: airheatman, HVAC Technician replied 11 months ago

Yes if board has a fuse, that should be sufficient.Hopefully replacing transformer will solve issue

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Customer reply replied 10 months ago
That got me going at the time. A/C worked great. Furnace motor is turning the blower and circulating air. However, now that the temperature is dropping, I have noticed that there is no heat. The igniter is not glowing. I ran a continuity test on the igniter and got a reading of 48. Using my voltage tester, I don't seem to have voltage going to the igniter. I traced the wires back and there is no power coming off of a set of 3 wires right beside where I plugged the black wire back in from the transformer. The 3 wires are labeled LO, HI and HSI, 2 are black and 1 is red. I believe 1 of those black wires leads to my igniter.
Customer reply replied 10 months ago
I don't get any reading. (I am assuming I can put my black probe on any of the neutrals?)
Customer reply replied 10 months ago
my LED is just blinking steady.
HVAC Technician: airheatman, HVAC Technician replied 10 months ago

Souds like board is bad. It should either send 120 to igniter or give an error code telling why not.

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Customer reply replied 10 months ago
Is there a chance I connected 1 of the wires from the transformer to a wrong spot? Seems everything is working except the ignitor
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