Home ac on the fritz again.......

[ram_man]

There is no power at the thermostat.

 

[ram_man]

I also don't have power at the sides of the contactor yellow and brown wire.

 

[EA82]

Low voltage problem, make sure the fuse is not blown, check if line voltage is going in the transformer and check if 24v is coming out, you mentioned that you replaced the transformer once, wouldn't be surprised if it blew again,probably power surges.

 

[ram_man]

I'm pretty positive the transformer is bad again. But would I then be suspect to a wiring issue that's causing it to blow?

 

[Fleetmon]

I would look at the wiring before replacing the transformer again...probably a wire shorted out. Check the wiring at the condensor unit real close....as mentioned, weed eaters and critters can shred wiring....also check the wires where they enter the unit.

 

[Amkeer]

Call in a expert to fix or if it is more than 10 years old replace it.

 

[SHOZ]

The thermostat usually gets power from a 120>24V transformer at the furnace unit. You should have 24V at the thermostat and if don't then go to the transformer at the furnace, it's probably open on the 24v side.

 

[chemman]

I went through something similar to this with my Rheem gas furnace/central air system a few months back. In short, check the resistance of the AC power contactor primary side (where the 24 V AC connects) inside the AC unit. If the resistance is outside of specified resistance range by even a few tenths of an ohm, the contactor is likely bad and will need to be replaced.

The 24 V AC from the transformer is used to power the control circuits in your system - thermostat, relays, contactors, etc., and if something pulls too much current through the 24 V AC transformer, the primary of the 24 V AC transformer will open like a fuse killing the system. No fan for the furnace, no power to the thermostat, no "low voltage low current" to operate the main power contactor in the AC unit.

I was told that in older, say over 12 years old, Rheem/Rudd systems, the 24 V AC transformer was used as a sacrificial fuse to protect the AC unit when the AC's contactor went bad. Newer systems and current OEM replacement transformers use a 1 or 2 amp fuse inline with the 24 VAC transformer's primary circuit rather than sacrificing the transformer.

Hope this helps.