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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by on July 21, 2006, 6:44 pm
My AC has been blown a few transformers, so obviously there is
something wrong in the units. I have tested all the control wires for
shorts, and the fans, blowers, switches and coils for shorts. Nothing
reads below 500 ohms, except for the 24v power leads to the board, that
reads 9ohms. At 24v/9 ohms that about maxes out the transformer. So I
guess my question is.. Is 9 ohms a bad reading at the control board and
can there be a short in the board that still lets the system run but
burns out a transformer in about 10 days? Oh and the control board does
not show any bad error codes.
Thanks
Todd
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Posted by Speedy Jim on July 21, 2006, 7:26 pm
TDHetrick@gmail.com wrote:
> My AC has been blown a few transformers, so obviously there is
> something wrong in the units. I have tested all the control wires for
> shorts, and the fans, blowers, switches and coils for shorts. Nothing
> reads below 500 ohms, except for the 24v power leads to the board, that
> reads 9ohms. At 24v/9 ohms that about maxes out the transformer. So I
> guess my question is.. Is 9 ohms a bad reading at the control board and
> can there be a short in the board that still lets the system run but
> burns out a transformer in about 10 days? Oh and the control board does
> not show any bad error codes.
>
> Thanks
>
> Todd
>
Boy, I guess that *does* overload the xfmr!
Not the HVAC expert, but I wonder if the board has
an MOV on the 24V bus and the MOV might be shorted.
Or a filter cap after the bridge rectifier shorted.
Unsolder stuff like that and measure again?
Jim
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Posted by CJT on July 21, 2006, 8:07 pm
TDHetrick@gmail.com wrote:
> My AC has been blown a few transformers, so obviously there is
> something wrong in the units. I have tested all the control wires for
> shorts, and the fans, blowers, switches and coils for shorts. Nothing
> reads below 500 ohms, except for the 24v power leads to the board, that
> reads 9ohms. At 24v/9 ohms that about maxes out the transformer. So I
> guess my question is.. Is 9 ohms a bad reading at the control board and
> can there be a short in the board that still lets the system run but
> burns out a transformer in about 10 days? Oh and the control board does
> not show any bad error codes.
>
> Thanks
>
> Todd
>
Are you sure the transformer is sized correctly? Maybe you need a
bigger one.
--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.
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Posted by on July 21, 2006, 8:39 pm
> >
> Are you sure the transformer is sized correctly? Maybe you need a
> bigger one.
>
> --
I am pretty sure it's sized right because one of the replacements that
burnt out was the same part as the origonal which had been working for
about 10 years.
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Posted by mm on July 22, 2006, 12:01 am
On 21 Jul 2006 15:44:59 -0700, TDHetrick@gmail.com wrote:
>My AC has been blown a few transformers, so obviously there is
>something wrong in the units. I have tested all the control wires for
What are the times between installation and blowing out, first one
first, through last. Estimates at least. So far I don't know if you
are talking about 3 months or 3 minutes.
If they last a month and the thing works, well something has almost
failed, or maybe one of the 4 diodes in the bridge rectifier has
failed.
>shorts, and the fans, blowers, switches and coils for shorts. Nothing
>reads below 500 ohms, except for the 24v power leads to the board, that
>reads 9ohms. At 24v/9 ohms that about maxes out the transformer. So I
>guess my question is.. Is 9 ohms a bad reading at the control board and
>can there be a short in the board that still lets the system run but
>burns out a transformer in about 10 days? Oh and the control board does
>not show any bad error codes.
Usually the first parts the AC current encounters in a transistor
board is a bridge rectifier, either 4 diodes arranged in a square**,
with input on 2 opposite corners and output on the other two corners.
Besides the parts the other guys mentioned, if one of those diodes is
shorted, that would be bad. Did you measure the resistance in both
directions? If it is higher in the other direction, that would be a
clue that the once symmetric bridge rectifier is now asymmetric,
because one of the 4 diodes is shorted. When good they aren't zero
and infinite in the two directions. They are low and high. When bad,
they are probably low and low. You might ask for more help on
sci.electronics.repair . They are nice there too.
You may have to do some unsoldering too measure these things, because
the circuit is not a simple rectangle, like in first electric classes.
**If it's not 4 separate diodes, it could be diodes in one little box
(with 4 leads.) I don't know how hard it is to find these, but you
can just use 4 separate diodes to replace them. It gets confusing
which direction each of 4 point
My transformer burned out the first July 4 weekend I lived here, when
I had 3 guests.
I couldn't get just a replacement trasformer that fit the original
place, so I had to buy a bigger one and mount it somewhere else. Has
lasted 23 years. I didn't do any testing though, beyong testing the
output of the xformer, which was dead. So I'm not saying a bigger one
would work better. But maybe one would. ask on the other ng.
>
>Thanks
>
>Todd
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