Question about Heating & Cooling

2 Answers

My thermostat has no power

.I have no power to my thermostat and after testing the out wires of the transformer i only have 19.4 volts??? Does this mean this is my problem? Also there is a flashing led light in my heat pump that is showing an error message of (secondary voltage fuse is open..)

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  • woockman1 May 03, 2010

    Yes the problem was the fuse on the circuit board... i checked the fuse on the circuit board outside the furnace(which was fine) and didn't realize there was another circuit board with another fuse inside the furnace itself(which was blown)...

    Appreciate the help both of you

  • woockman1 May 09, 2010

    there was a internal circuit board fuse blown...i replaced it...the thermostat came back on the fan kicked in...but when i switched it to auto heat nothing....then lost power again...and both internal circuit board fuse and external circuit board fuse were blown...

  • woockman1 May 09, 2010

    I do have a multimeter but i am a novice with it..clear explanation of how to test wires would be appreciated...also currently i replaced the two blown fuses and now the LED error light is on continuously but i have no power to the thermostat..don't know if that helps

  • woockman1 May 09, 2010

    Also not sure if it matters but i was wrong it is a natural gas furnace..

    Payne

    Model number PG9MAA036080

  • woockman1 May 09, 2010

    I had 27 volts between common and red on thermostat

  • woockman1 May 09, 2010

    it is a payne model number pg9maa036080...i believe natural gas furnace.

  • woockman1 May 09, 2010

    Brand: PAYNE HEATING & COOLING
    Manufacturer: CARRIER CORPORATION
    Model Number: PG9MAA036080**
    Fuel: Natural Gas
    Input Capacity: 80,000 BTUH
    Output Capacity: 74,000 BTUH
    Efficiency: 90 % AFUE

    Energy Star Qualified: yes
    Air Flow Configuration: Horizontal and Up and Down
    Electrical Phase: Single-phase
    Combustion Type: Condensing

  • woockman1 May 09, 2010

    http://www.docs.hvacpartners.com/idc/gro...

    This is a newer model of what i have, but they are very similar

  • woockman1 May 10, 2010

    I can try to get the schematic tonight...

    I do have a heat pump with nat gas back up as u thought...

    Could this be a bad contactor? was reading online someone with simalar problem was the contactor?

  • woockman1 May 10, 2010

    Also drain is working and no compenents are wet..

  • woockman1 May 11, 2010

    Well upon looking closer at the condensing unit wiring, I found a yellow wire that was touching a ending metal hook up to another wire, when i pulled it back sure enough it had been worn through....VICTORY!

    I appreciate all the info you gave me...thank you for the effort...u were right from the beginning but i didn't look close enough outside...

  • Brian Niten May 11, 2010

    Is there a fuse on the circuit board? I would check for that first then concentrate on the transformer.

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It sounds like you have a short or a ground in the control circuit. Somtimes you can spot a bad component with your eyes. Look at the different relays to see if any looked burned. You might also look for a wire that has came off and is touching ground. You mentioned you put it in auto heat. This could narrow your search to components for heating. The problem could be in the coil on your reversing valve. I don't know if you have any trouble shooting experience, but if you have a multimeter you could do some resistance checks to find the problem.

Posted on May 09, 2010

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  • Brian Niten May 09, 2010

    Remove the thermostat face and check for 24vac between the R & C terminals on the thermostat.

  • Brian Niten May 09, 2010

    Good, the transformer is still working. Do you have a schematic you can send me or can you read the schematic? If you can locate the transformer and determine which part of the schematic is the low voltage side and then we can go through component by component to locate your problem.

  • Brian Niten May 09, 2010

    What kind of setup do you have? Is it a/c and natural gas heat or a heat pump with natural gas backup?

  • Brian Niten May 09, 2010

    That doesn't include the electrical schematic. Look on the door for you unit and see if it has one on it. I see from you link that you have a condensing furnace. Make sure the drain is working and also check for any electrical components that may have gotten wet. Let me know if you can find a schematic attached to your furnace.

  • Brian Niten May 10, 2010

    I'm not sure. I'm thinking your problem is in the 24v circuit which could be the coil that pulls the contactor in. You can remove the 24v wires from the contactor and use your meter to ohm the coil. Turn off the 240v first so you don't accidentally get shocked.

  • Brian Niten May 11, 2010

    Good job. Patience pays off in the long run.

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Assuming you are talking about a transformer that puts out secondary voltage of 24V (and I think you are) - then your voltage reading at the transformer is within guidelines.

The flashing red light seems to be telling you that you have a fuse blown in your secondary voltage circuit which under normal circumstances would disable your t-stat. I would try and find a fuse in that circuit and check and see if it is good or not.

If it is bad - you need to replace it - but you also need to determine what blew the fuse.

Sometimes fuses blow on their own and the reason cannot be determined, but most of the time there is a reason that the fuse blew in the first place.

It may be that you need an experienced troubleshooter to figure out your problem but I would at least try replacing the fuse and see if the unit operates properly from that point on.

If it blows another fuse then you will need someone to trouble-shoot the problem or submit more information to this site for some additional help.

good luck!

Posted on May 03, 2010

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1 Answer

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by doing this if the fan motor operates you know that the High voltage & the low voltage (24 volt control power) are present.
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With 2 transformers one for indoor unit
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R = Red One Side of 24 volt Transformer
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2 Answers

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My ac unit does not have power to the thermostat. There is 200 volts going into the transformer and 24 volts going out. There is 24 volts on the back side of a terminal with thermostat wire running to the...


Please exercise due caution in checking voltages in live circuits!

24 volts sourced by the transformer, through the thermostat, then through the contactor (turns on power to compressor/fan) and returns to the transformer, If the thermostat is closed (calling for cool) you will see no voltage across it, but instead the contactor should be energized. Please note, 200 volts seems odd, you should have between 215 and 235. It sounds more like the contactor relay coil may be open. Is the contactor/transformer one piece?

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CARRIER AIR CONDITIONER/HEAT PUMP PROBLEM WOULD NOT RESPOND TO THERMOSTAT. UNIT IS AT LAKE HOUSE WHERE WE DO HAVE BAD STORMS. IN CHECKING, INSIDE PART OF UNIT HAD BURNED UP THE TRANSFORMER BUT NOT...


what I have always been told is if your 24 volt side burns out check the high volt side if the hi volt side burns out check the low volt side.

A quick way if the primary side is burningout due to a problem with the low volt side:
1 MArk all the thermostat wires at the indoor unit
2 Disconnect them at the indoor unit.
3 Check main line voltage before proceeding (A 208 volt is not considered 220V and 240v Is not considered 208V> In these circumstances the voltage may have changed with the power company replacing a transformer and now you need to change the main power input lines at your control transformer for the correct operating voltage). If okj then proceed:

4 If you have an amp meter attach it to one of the lines going to the transformer.
5 Apply main power and listen for hum, note if smell starts again and if so problem has to be in board or main incoming voltage too high or too low. Amp draw should be less than 3 amps.
6 If your to this point and still havent found any trouble in the above as of yet, Connect the wire marked "C" together. Then just touch the thermostat wires one at a time to the places where they go on the indoor unit and watch the amp meter. If you donmt see the meter jump the circut is probably ok but leave them disconnected until you touch all of them to the correct place or wire. Here is a possible problem I ahve seen a thermostat wireing problem if the wires are stripped too far and a "whisker" of the wire sticks out and allowes one of the other wires to cross short out. In this case just cut off the excess wire or bend it over out of the way asnd continue with the test. You can always cut it off later after the tests. If you see the meter jump up and stay up and /or blowes the fuse the wire that you used and it blew is where to consentrate.
7 No wiring problem found means that you could have a relay or contactor not pulling in properly.
and this will cause the amp draw to go way over the transformers power out put or VA rating.
8 Inspect the thermostat wiring for the "whisker" I mentioned above.
9 If you have done this to the end of the thermostat wires and your main incomming voltage is correctly wired in on the transformer andf your relays and contactors are pulling in evenly and not delaying excessively your problem should be fixed.

If this helps you please rate me as high as you can and thank you for using fixya.

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