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All components in my hvac system were replaced a little over a year ago. When we tried to turn on the heat this past winter it wasn't working and turned out to be a faulty control board in the furnace. It was replaced and heat operated properly for the remainder of the winter. The entire system was off for several months. Now, when I attempt to turn on the AC I get no response from the unit. Nothing is blowing out of vents, even when fan mode is set to on. So far I have done the following: replaced air filter, reset every breaker in my panel, turned furnace switch on and off twice in thirty seconds, replaced thermostat batteries, reset thermostat programming and turned power off at disconnect to condenser and then back on again- all to no avail. There is no LED light blinking where it should be on the furnace (to indicate problem code or normal operation) which means there is no power to the unit. But if there are no tripped breakers and the furnace switch is 'on' then where else could the problem be originating? The thermostat works fine when switched out with upstairs units thermostat.
Additional: Furnace- American Standard Single Stage Freedom 90 Gas Furnace AUC 1B080A9421AD
Thermostat- Pro1aq T705
The easy check is the circuit breakers. There are often exterior and interior cut off switches too. Maybe one got flipped. If that does not prove productive you gotta call the folks that installed the thing.
As Chet was alluding to, you have the 220V breakers or fuses in the main panel box which is normally outside. I'd check those to make sure it's on and properly marked. When you had the new unit installed, the A/C tech should have replaced it with the correct size. You also have a subpanel box that is inside. Around here they are found in the garage but may be else where like a closet, etc. This box will usually have a bunch pf breakers in it for all of the branch circuitry. If the fan in the unit runs but doesn't cool, you also have a breaker at the unit outside, if the tech installed it correctly. Code says it has to be within 5 feet of the unit. If this doesn't get it running, call a professional. You may have a weak breaker and it needs to be replaced. You may also have a loose wire that can cause a fire. There's a lot of variables but it's something you need to be cautious of. Anytime the power is out to a circuit, it really should be looked at by a pro....or make sure the fire insurance coverage is high and paid for.
...you have the 220V breakers or fuses in the main panel box which is normally outside.
Not true- A main disconnect on the exterior is required today, but that may have not been the case when OP's house was built.
You also have a subpanel box that is inside.
It's not a "sub-panel" it would be the main breaker/fuse panel.
If the fan in the unit runs but doesn't cool, you also have a breaker at the unit outside, if the tech installed it correctly.
If you have a breaker/fuse in the main panel, why would you ALSO have breakers/fuses outside- Wrong! If there are breakers/fuses in the main panel, there are "disconnects" at the unit. If there are NO breakers/fuses in the main panel they will be at the unit(s).
Code says it has to be within 5 feet of the unit.
You can check to see if there is power to the unit by plugging another small electrical device into the outlet serving the furnace, that will confirm whether or not there is electricity there. If there is electricity at the outlet, then you may be looking at the mobo again, there may be fuses there...could be a problematic model etc..
Typical MAIN panel box as per requirements of the second largest electrical supplier in the Southwest.
Inside the MAIN panel box. Note breakers for 220V only in this box which are the range/stove, A/C compressor in this case, and to the subpanel box.
Typical SUB panel box as accepted by the second largest electrical supplier in Texas. This one is in the garage which is fairly typical for new construction. Note double breaker on lower left of box.
Typical air handler installation. All residential air handlers are 110V, just like this one. Note 110v duplex receptacle for power.
In the case of this house, there is no breaker at the compressor as the unit is within 5ft of the main panel box. Otherwise, a correct breaker of the correct size is required by code in a box no farther than 5 ft from the compressor. You may substitute a breaker cutoff which is a handle affair that all you have top do is pull it and the handle comes out cutting off the electricity. They are a one time use part and the entire unit replaced if you pull it. Breakers are reusable and in the case of these units, provide additional backup and convenience of being able to turn the unit off and on without cost.
Not all air handlers run on only 120 volts. There are plenty that are 208-240 volts.
OP - Sounds like a fuse is blown that protects your transformer if none of the breakers are tripping. Sucks but you shouldn't just go replace the fuse, you may have a low voltage short somewhere. Without being there there's not much more we can do for you.
Last edited by BigJon3475; 07-02-2012 at 09:20 PM..
Not all resiudential AHU's are 120vac, only gas heat ones. Electric heat AHU's are 240vac. A CU disconnect box can have either a breaker or a reusable pull out plug.
You can check to see if there is power to the unit by plugging another small electrical device into the outlet serving the furnace, that will confirm whether or not there is electricity there. If there is electricity at the outlet, then you may be looking at the mobo again, there may be fuses there...could be a problematic model etc..
Furnaces generally don't plug into a wall receptcale.
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