A/c blower control question?

I have a short. The secondary on my transformer is dead. Do I need to install a new one prior to testing for a short? Also, what wires do I disconnect to test for a short? I plan on installing an in-line fuse.





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Here's what I see.


XFMR-R connects to transformer


R connects to t-stat


XFMR-C connects to transformer


C connects to the pump relay


G connects to t-stat





Thanks!A/c blower control question?
Don't install a new one until you have repaired the short,or the new one will smoke and burn up.


You have to OHM OUT ALL 24 volt components and 24 volt wiring.


The ohms are missing in the problem wires because there IS A SHORT and the current is BYPASSING the normal route,creating less ohms and smoking the transformer.





More often than not when I have had a transformer burn up,it is due to 24 volt wire shorting out against the cabinet.





They do make a control transformer with a tiny 3 amp circuit breaker on it.The transformer won't burn up when over amped,the 3 amp circuit breaker will pop and you simply reset it.You should buy one like that.





Sometimes shorts are hard to locate and take considerable time to locate.


You have to start a process elimination. For instance,contactor coil and the 24 volts wiring,blower relay coil and 24 volt wiring,reversing valve coil and 24 volt wiring,thermostat wiring,all 24 volt wiring in the indoor unit,and all 24 volt wiring in the outdoor unit.





Check one at a time and write down the ohm readings.


The low ohm reading will be the problem.





Good luckA/c blower control question?
Just because your transforer is not putting out a secondary voltage does not mean that you have developed a short. Transformers do have a life-span. They commonly fail. It can be hard to diagnose the problem without a working transformer. Some of the transformers have a fuse or a reset switch. I would replace the transformer and wire an amp meter in series with the one of the leads on the secondary. You can do this at the thermostat with the red wire. Then slowly go through each selection (Fan, AC, Heat etc...) If you see a spike in current turn it off real quick and you have found your short. If it's a 40va transformer then you shold not really see more than about 0.5 amps. Much more than that you are are going to start burning up your transformer. It usually only runs a couple relay coils and/or a small printed circuit board.






In my forty + years as a repair I have found most times it is the outside a/c contacter drawing to much power causing the transformer to burn. Check to see if the Contactor coil on the unit is bad. That would be my first check. Another would be a mouse, dog(puppy) cat. Eating your t-stat wires this will also cause a short and this is really hard to find. Generally in the raceway between the inside unit and OS unit.


Yes I would install a 2 amp fuse in line or a mini breaker. Use a low amp reading amp meter to help evaluate the problem.
Hmmm...Interesting. Are you sure you have a short? If the secondary of the transformer is dead, maybe the primary is too. Did you check that already? Email me, and maybe we can chat about it online.

make up