question for HVAC guys

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RedFish

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We have a no heat problem...
First to detail this system... All electric, air handler in a closet setting, heat section on top, then blower, vaporator coil , return air underneath.
A/C condenser outdoors of course.
The condition...
Call for a/c and spark appears at thermostat mercury bulb ( normal ) condenser unit starts, blower in air handler does not.
Call for heat and absolutely nothing, not even the spark at bulb ( not normal ).
Call for fan only gets no response either.
Is most likely culprit blower motor failure ?
TIA
 
if the fan is not running you can jump it out - Depending on your setup the green wire is usually the fan - that needs to have 24 volts ( if you have a low voltage setup ) and if it does not you can jump it out from the common ( power ) to see if the fan runs - it can be jumped out for temp heat if that works.
 
DJVCUDA said:
if the fan is not running you can jump it out - Depending on your setup the green wire is usually the fan - that needs to have 24 volts ( if you have a low voltage setup ) and if it does not you can jump it out from the common ( power ) to see if the fan runs - it can be jumped out for temp heat if that works.
Click to expand...

It is a low voltage thermostat. There is a controller board in the closet too.
Green wire jumped to which/what ?
 
check and make sure you have 24 volts Your 24 volt transformer that controls your
thermostat may have went south on you RedFish
 
if its low voltage get a meter -

Like mike said - check and see if the common has 24 volts when you ground it through the meter.

if it does
check the green wire for voltage when it calls for fan

if it does not then jump it out and give it 24 volts to see if the fan will run.


this is all dependant on what type of setup you have - but this is the most common, and low voltage as well.
 
I cant find 24 volt reading at the thermostat. Actually found nothing more than some random readings. There is current there though otherwise the bulb wouldn't arc compressor and fan outside wouldn't start.
I dread going into the closet. I'll need to get a box, pull all the wifes stuff from the shadow box, then pull the shadow box. Grrrrr
 

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If it helps.... 4 wire thermostat, red, green, yellow, white, and OEM jumper from those marked 1 and 2 on its backside.
 
post a pic of your stat connection to the wall
 
You may get lucky RedFish, some times the 24 volt small transformer is out side in the condenser, shut the power off to the outside unit (should be a pull station out there) and open the control panel and look in side and hopefully you will see a transformer :cheers:an easy cheep fix :cheers:
 
pitiful pic, went for second shot and camera says memory full. Wife would beat me if I delete anything :(
 

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UPDATE after probing all about on the thermostat, BAM ! heat is on and running.
Now I'm wondering if there is a start cap' failing at the blower motor.
 
I switched it off since the thermostat cant function properly dangling out of level.
Don't know whats my next move. I hate for stuff to start working before I fix it LOL
 
Oklacarcollecto said:
Maybe the thermostat is bad?
Click to expand...

That would be the easiest R&R. Fan only selection also works now.
Probing all around shows no discernible voltage at the thermostat but I know its there. \me scratches head
 
Seems to be working fine. Maybe it wont fail again...
before 3:AM anyway. I'm cooking a pot of beans just in case.
 
Well I'm "late to the game," LOL

If you can post some photos of the inside of the furnace control panel, that would help, and of course the model no

Here, generally is what happens in an electric furnace. Most "old school" electric furnaces have a set of breakers in / on the furnace itself. These can of course trip, obviously not the problem here.

The stat is supplied 24V from the red wire, coming from the transformer. red to white switches on heat, Red to green brings on the blower, for AC and for "summer fan" (blower only) and red to green (blower) added to Red to yellow brings on the condensing unit

Usually red to green should bring the blower on instantly, IE a relay and not a sequencer. However, this is NOT what brings the blower on for heat. In heating, normally only red to white is made, and the blower comes on delayed. In some units, the blower is delayed by a sequencer, in some, brought on by a temperature switch (fan switch) and in newer units, controlled by a solid state board......delayed.

Electrics are normally "staged" so that the heating elements come on one's or two's at at time, devices known as "heat sequencers." These, really, are somewhat reliable, and somewhat troublesome. All these things are, simply, are a 24V heating element, with a thermal switch on top. Depending on how many elements in the furnace, you might have a couple, or several, and some are double pole

The thermostat normally runs one or two sequencers, many times one, and that sequencer "daisy chains" to fire the next sequencer. When the element in the sequencer, triggered by the wall stat heats up, the thermal disc switch on top trips shut and turns on the blower and the first set of elements. When the next sequencer closes, then the next set of one or two elements kicks in.

Any how after all this ranting, what happens is THESE THINGS FAIL and get sticky and intermittent. Here's a working diagram of one:

Bottom most connections are the 24V heater, top set is last to switch, and middle set is contacts which close first

sequenceside.jpg


2005-9-8_sequencer_2_w550.JPG
 
OK ( it has failed again btw )
How this system operates...
Calling for heat brings the blower on instantly, always has anyway. The blower continues to run for a period after the heat strips have went off.
I don't think the electric heat section should come on without the controller having a blower runs signal in place for safety reasons.

While I was typing above the blower suddenly started again. I'm starting to think its intermittent blower motor failure. In any case I'm going into that closet :(
Shadow box for access door was a great idea when I was younger.
 
Unless the motor is heating due to something like dragging bearings, and tripping an overload, an intermittent motor is unlikely. Much more likely to be a bad relay, sequencer, or if newer and a single control board, "something on the board"

There is normally no proving for blowers in older electric furnaces. The elements normally have individual hi limit thermostats, in series with one time protectors. These look like diodes, and are thermal fuses.

A diagram of the thing would tell the story. I know you don't want to hear this, but for safety reasons..........as well as keeping the service guy in a good mood, LOL........it's REALLY not a good idea to "lock up" access to a furnace
 
Air Handler is American Standard ( TRANE )
Model TWV036B 140A 1
 
Here's the deal.. heat and air switched off fan switch does ON and AUTO. Switch from on to auto and it runs on a time ( normal ).
Once the fan stops, I switch to on again,,no response.
Tap the corner of the control box with screw driver handle once and the fan starts right away.
 

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That is the air handler WITHOUT installed heater which should yet have another number

Here's the closest I can find for a manual:

http://hvac-talk.com/vbb/attachment.php?attachmentid=249911&d=1331261139

The diagram page 20 for the blower relay shows a "PCB" and an "FDR" so I don't know if it's a simple delay relay mounted on a PC board or if there's additional circuits on the board not shown.

EDIT just saw your last post. I'd about bet money, Red, that there's a sequencer in there that's getting intermittent. Typical.
 
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