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My unit keeps blowing out the 240/24volt Transformer. The fuse on the control card is good.The unit on heat,will cycle to 3 minutes to full flame and blower then shuts off. I have 2 blinks and 6 blinks on circuitboard

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If the transformer is burning out the problem is in the wiring from the thermostat to the transformer. There has to be two wires that are touching each other or the wires are grounding. You might also check the polarity of the furnace to see if the electricity is going into the furnace the way that it is designed to. Check the back of the furnace cover where the control panel is and see if there isn't a listed code for the blinking lights most furnaces have this code sheet on the inside cover. If there isn't a code sheet you may be able to get one e-mailed to you by the manufacturer of the furnace or contact a local a/c repair shop I'm sure they would have a code sheet.

Good Luck


Posted on Nov 17, 2009

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Coleman furnace dgaa077bdta

The control fuses keep blowing tells me one or more of the control that operate the control on 24 volts is malfuctioning. Most controls operate at about 5 watts and on a clamp on amp meter normally pull about 0.2 amp (p = current x voltage, 5 watts = 0.2 amps x 25 volts) I install 75 watt 24 volt transformer with a resettable overload to save on fuses. I reset the transformer and quickly go to the controls and determine the amp draw. When I find the one >0.2 amps I found the problem. The things to check is the emergency heat sequencer, fan control sequencer, reversing valve for heat pumps, main contactor on the condensing unit and any other 24 volt control loads. I have had to replace the themostat wire because the increase current for the thermostat wire can cause the entire length of wire to form a long heater and cause insulation degradationa and cause the thermostat wire to short out and blow the fuses.
Hope this helps

Aug 30, 2014 | Coleman Mobile Modular Home Gas Furnace...


Troubleshooting Guide

  • Problem: Totally dead oven.
    Possible causes:
    1. No power to outlet (blown fuse or tripped breaker or GFCI).
    2. Blown main fuse - likely due to other problems.
    3. Open thermal protector or thermal fuse.
    4. Defective controller or its power supply.
    5. Clock needs to be set before other functions will operate (some models).

  • Problem: Totally dead oven after repair.
    Possible causes:
    1. Cabinet screws replaced in incorrect location (safety interlock not engaged).
    2. Any number of screwups. :)

  • Problem: No response to any buttons on touchpad.
    Possible causes:
    1. Door is not closed (some models).
    2. You waited to long (open and close door to wake it up).
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Defective interlock switches.
    5. Faulty controller or its power supply.
    6. Touchpad or controller board contaminated by overenthusiastic cleaning.
    7. Defective/damaged touchpad.

  • Problem: Oven runs when door is still open.
    Possible causes:
    1. Damaged interlock assembly.
    2. Cooling fans (only) running due to bad sensor or still warm.

  • Problem: Oven starts on its own as soon as door is closed.
    Possible causes:
    1. Defective triac or relay.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.

  • Problem: Oven works but display is blank.
    Possible causes:
    1. Defective controller or its power supply.
    2. Broken display panel.
    3. Oven needs to be reset (pull plug for a minute or two to reset).

  • Problem: Whacked out controller or incorrect operation.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Controller is confused (pull plug for a minute or two to reset).
    3. Defective controller or its power supply.
    4. Touchpad or controller board contaminated by overenthusiastic cleaning.
    5. Defective/damaged touchpad.
    6. Defective sensor (particulalry covection/mirowave combos).

  • Problem: Erratic behavior.
    Possible causes:
    1. Previous or multipart cook cycle not complete.
    2. Bad connections in controller or microwave generator.
    3. Faulty relay - primary (or HV side, much less commonly used).
    4. Defective controller or its power supply.
    5. Bad contacts/connections on mechanical timers. Intermittent fuse.
    6. Power surge at start of cook cycle confusing controller.
    7. Microwave (RF) leakage into electronics bay.

  • Problem: Some keys on the touchpad do not function or perform the wrong action.
    Possible causes:
    1. Touchpad or controller board contaminated by overenthusiastic cleaning.
    2. Defective/damaged touchpad.
    3. Controller is confused (pull plug for a minute or two to reset).
    4. Faulty controller.

  • Problem: Microwave oven does not respond to START button.
    Possible causes:
    1. Defective START button.
    2. Faulty interlock switches.
    3. Door is not securely closed.
    4. Faulty controller.
    5. You waited too long - open and close door to wake it up!

  • Problem: No heat but otherwise normal operation.
    Possible causes:
    1. Blown fuse in HV transformer primary circuit or HV fuse (if used).
    2. Bad connections (particularly to magnetron filament).
    3. Open thermal protector or thermal fuse.
    4. Open HV capacitor, HV diode, HV transformer, or magnetron filament.
    5. Shorted HV diode, HV capacitor (will blow a fuse), or magnetron.
    6. Defective HV relay (not commonly used).

  • Problem: Timer and light work but no heat, cooling fan, or turntable rotation.
    Possible causes:
    1. Defective (lower) door interlock switch or door not closing fully.
    2. Faulty relay or triac.

  • Problem: Fuse blows when closing or opening door:
    Possible causes:
    1. Defective door interlock switch(s).
    2. Interlock switch knocked out of position.
    3. Misaligned door.

  • Problem: Loud hum and/or burning smell when attempting to cook.
    Possible causes:
    1. Shorted HV diode, magnetron.
    2. Burnt carbonized food in or above oven chamber.
    3. Shorted winding in HV transformer.
    4. Frayed insulation on HV wiring.

  • Problem: Arcing in or above oven chamber.
    Possible causes:
    1. Burnt carbonized food deposits.
    2. Exposed sharp metal edges.

  • Problem: Fuse blows when initiating cook cycle.
    Possible causes:
    1. Defective interlock switches or misaligned door.
    2. Shorted HV capacitor.
    3. Shorted HV diode.
    4. Shorted magnetron (probably won't blow main fuse but HV fuse if used).
    5. Defective triac.
    6. Old age or power surges.
    7. Defective HV transformer.
    8. Short in wiring due to vibration or poor manufacturing.

  • Problem: Fuse blows when microwave shuts off (during or at end of cook cycle).
    Possible causes:
    1. Defective triac (doesn't turn off properly).
    2. Defective relay.
    3. Shorting wires.

  • Problem: Oven heats on high setting regardless of power setting.
    Possible causes:
    1. Faulty primary relay or triac or HV relay (not commonly used).
    2. Faulty controller.

  • Problem: Oven immediately starts to cook when door is closed.
    Possible causes:
    1. Shorted relay or triac.
    2. Faulty controller.

  • Problem: Oven heats but power seems low or erratic.
    Possible causes:
    1. Low line voltage.
    2. Magnetron with low emission.
    3. Faulty controller or set for wrong mode.
    4. Stirrer (or turntable) not working.
    5. Intermittent connections to magnetron filament or elsewhere.
    6. Faulty primary relay or triac or HV relay (not commonly used).

  • Problem: Oven heats but shuts off randomly.
    Possible causes:
    1. Overheating due to blocked air vents or inoperative cooling fan.
    2. Overheating due to bad magnetron.
    3. Bad connections in controller or microwave generator.
    4. Faulty interlock switch or marginal door alignment.
    5. Faulty controller.
    6. Overheating due to extremely high line voltage.
    7. Stuck stirrer fan resulting hot spots detected by sensors.

  • Problem: Oven makes (possibly erratic) buzzing noise when heating.
    Possible causes:
    1. Fan blades hitting support or shroud.
    2. Vibrating sheet metal.
    3. Vibrating transformer laminations.
    4. Turntable or stirrer hitting some debris.

  • Problem: Oven light does not work.
    Possible causes:
    1. Burnt out bulb :-).
    2. Bad connections.

  • Problem: Fans or turntables that do not work.
    Possible causes:
    1. Gummed up lubrication or bad motor bearing(s).
    2. Loose or broken belt.
    3. Bad motor.
    4. Bad thermostat.
    5. Bad connections.

on Mar 30, 2008 | Kenmore 80412 Microwave Oven

1 Answer

Furnace lights blows heat in cycle, pops sensor on blower and continuosly blows air until button on sensor is pushed back in

If the sensor knocks the unit off and the the fan keeps blowing without a flame ,the limit (the sensor is a limit comptroller that turns off flame @ a set temp and allows the fan to run until the heat exchanger cools to @ set temp) has out lived its lifetime and needs to be replaced.the button is a manual reset that once reset would allow the unit to continue to run flame and blower at the same time after having been set once, if it is an ongoing problem and needs to be reset more than once then replace the limit control (sensor) in kind. (With the same mode and set-points for the limits)

Oct 25, 2012 | Intertherm 56000 Btu Gas Furnace

2 Answers

BDP Heat Pump Transformer Keeps Blowing

Should have a 5 amp fuse on red wire in between transformer and tstat. If not put one. This will protect transformer. Turn power off and take a good picture of tstat wiring. Remove all wires to the tstat. With the air handler wires join fan and red. (Likely green) let run. Then add compressor and reversing valve ( if reversing valve is energized in cooling ) which in most cases it is. Should then have cold air. Let run. If no problems you know it's outside of the machine. Tstat or wiring. Hook inside of machine all back up to tstat wires. Do the same thing with the tstat wire inside the thermostat. If no problems, must be bad tstat. Hook everything back up right. If fuse blows or transformer because you didn't put the fuse, then you know for sure it's the stat. Good Luck

Mar 15, 2017 | Heating & Cooling

1 Answer

Have a goodman central air unit, non heat pump. keeps smoking transformers, on the inside unit, replaced fan capacitor and transformer as the old transformer was smoked as well. But to no avail the new...

There is a short in the control wiring that needs to be tracked down. Ohm the wiring to the low voltage controls, ie thermostat wiring and thermostat. Try disconnecting the thermostat wires to rule out the problem in the control wiring to the thermostat or thermostat itself, then install a new transformer without connecting the thermostat wiring, jump the red and green wire at the unit low voltage connections to test blower, and then add yellow for compressor, should be no more than 3 amps on control side wiring with A/C on.
If the problems still exists without the thermostat wiring connected then there is a problem in the wiring in the unit or control board itself.

Aug 24, 2011 | Heating & Cooling

2 Answers

The heat was working and then i turned it to cold and now the thermostat wont work and it is new cant get the heat or air to come on

Sounds like you had a direct short on the 24v side
of the transformer. Usually there is a inline fuse that
will blow so it protects the transformer..

Turn power off to unit
-Take doors off unit
-Look for a little fuse that may be located on the
control board where the thermostat wires go.

-Check the fuse, if it is blown then replace. However
you need to check the thermostat and the wires
that go to it to make sure they are not touching.

-If the fuse is not blown, then at the thermostat put
the fan to the on position. Go to the unit and turn the
power on, if the fans starts then things are at least
looking better. If the fan doesnt start, check to see
if the 110/220 fuse or breaker that you have isnt tripped

Jan 18, 2010 | Honeywell Programmable Thermostat Heater

2 Answers

Blown Transformer heat pump

blown transformers are usually from a low voltage short the first thing i would do is wire a automotive or resetable 3amp fuse in line with the transformer so you dont blow transformer after transformer the wire coming off the transformer that say 24v take that wire a couple of inches down and cut it and install the fuse in series there

now you can go through your low voltage wires one by one and test them unhook all the wires to your outdoor condenser at your indoor unit(furnace or airhandler) and try turning it to cool now if you blow the fuse the short is between the tstat and the indoor unit if the fuse is still good leave it on cool and hook up one wire at a time to your outdoor unit starting with R a lot of times your contactor or your defrost board will short out on you also look for pinches in wires wires with cracks in the insulation and wires touching metal this situation can be a real pain sometimes i would recommend calling a hvac company if you start to get stumped
hope this will help you

Jul 26, 2009 | Ruud UBHC Air Conditioner

2 Answers

One unit runs a while, powers down, other unit blows transformer

you say it keeps blowing the transformer? you mean circuit breaker? if it is the circuit breaker, have the wiring checked for a short, if no short do a ohm test on the compressor. it may have shorted out internaly.

May 31, 2009 | Haier HC48C1VAR Central Air Conditioner

1 Answer

Furnace is blowing but gas is going off and on all the time

Check the heat anticipator on the stat if its a manual one

Mar 16, 2009 | Heating & Cooling

1 Answer

Blows fuse for heat after about 30 minutes

yes , occassionally though it will run for full cycle ....but not very often

Sep 06, 2008 | Kenmore 73952 Gas Dryer

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