DIY Home Improvement, Remodeling & Repair Forum > Appliances > HVAC > Cant figure this out! Not getting 24v at the board or thermostat




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Old 03-09-2013, 05:46 PM  
kok328
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I'm pretty sure you've lost a leg of power on the 240V circuit and your meter is reading the backfeed from the remaining leg.



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Old 03-09-2013, 06:17 PM  
jayrod
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Quote:
Originally Posted by kok328 View Post
I'm pretty sure you've lost a leg of power on the 240V circuit and your meter is reading the backfeed from the remaining leg.
That would make the transformer short out or go bad or whatever happened? Because Ive gone through 2 now. Original one and a new one.


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Old 03-09-2013, 07:54 PM  
kok328
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It won't make it short out but, it would make it not produce 24V on the secondary.
Take either transformer (old or new) and hook it up to 120V using the white (neutral) and black (hot/120V) and test the secondary for 24V output. Chances are they both still work.

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Old 03-09-2013, 07:58 PM  
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Transformer doesnt work because I tried it on the working unit, and then that unit didnt work. No 24V. So either the Transformer was sold to me bad or I blew it.

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Old 03-09-2013, 07:59 PM  
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I'll still try that real quick

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Old 09-27-2013, 07:32 AM  
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Alright I still haven't resolved this and winter is coming fast! I haven't even touched it since. I do not want to blow another transformer so I would like to fuse the next one. Do I just fuse the red 24v wire coming out (the one going to the thermostat board) with a 3A or 5A fuse? Will that atleast keep me from blowing the transformer and just blow the fuse instead? Also, I was going to replace the contactor outside since its cheap. See if that fixes it.

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Old 09-27-2013, 02:00 PM  
nealtw
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You should research the thermostat and find the amps it requires.

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Old 09-27-2013, 02:29 PM  
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Yes but is that the correct spot to wire the fuse so it doesnt blow again?

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Old 09-27-2013, 02:56 PM  
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You would only have to fuse the wire carrying the voltage, if you have a short to ground a fuse on the other wire would not help.

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Old 10-28-2013, 04:52 PM  
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Okay I made some progress. I unscrewed the thermostat board and looked at the solder points on the back and one of the main ones that feeds the Transformer is burned up. The solder point is burned, looks like its not making a connection. The wire that goes to the burned solder point is the black main power wire coming into the house that goes to the heat sequencer, and then goes to the board labeled HEATER, and that's where the burned solder point is.

More general pics of what the unit looks like are on page 2.

The first pic is where the main power (black) wire comes into the house and splits into 3 wires going into the sequencer.

The 2nd pic shows the front of the board, and the HEATER connection. That's where the black wire leads to at this point. I had the whole connector unplugged at that point.

The 3rd pic shows the back of the board, and the burned connection. That connection feeds the T3 terminal that the Transformer plugs into to get 240 Volts, and also looks to feed the M2 part of the motor which I assume is where it gets its 240 volts. So what would cause the burned solder point?? Do I need a whole new board or can I just clean and resolder?

The 4th pic just shows the whole back view of the board.

Edit - Just had a thought. Since the blown point only leads to 2 connectors (T3 and M2), why cant I just bypass the board all together and connect the black wire to T3 and M2 at the same time? That would bypass the board and the burned solder point. Wouldn't that work?



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