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designSTL 07-01-2012 02:30 AM

1 year old HVAC system not working
I just bought this house a little over a year ago and at the time had all components of hvac system replaced (furnace/thermostat/ac). When we went to turn the heat on this past winter it wasn't working and turns out it was a faulty circuit board in the furnace which was then replaced. It worked perfectly for the remainder of winter. The system was off for several months in the interim and now when I go to turn on the ac its not working, neither is the fan or furnace. I hear the click at the thermostat when I turn it to cool and lower the temp but nothing happens- no air coming out of vents at all. I checked the air filter, main breaker, furnace breaker and replaced the batteries in the thermostat to no avail. The furnace is an American Standard Single Stage Freedom 90 Gas Furnace and the new thermostat is a Pro1AQ T705. Where should I be looking for a problem, in the thermostat or furnace? Or should I say where do I begin?

scottmcd9999 07-01-2012 05:16 AM

Check to be sure that you haven't tripped a breaker. You'd be looking for a single pole breaker (one handle, not two). Also be sure that you haven't turned any wall switches OFF - many times the furnace is powered by a simple light switch on the wall.

Have you removed the panels on the furnace? If you have, be SURE that you've put them back correctly. Furnaces have kill switches that turn the power off if the panels aren't put back correctly.

Outside of that, you might have a blown control fuse. If you can remove the panel on the furnace, look for that circuit board they replaced. Does it have an automotive-type fuse on it? If so, remove it and replace, if blown (you can get them at any auto parts store). However, fuses don't normally blow from being faulty, so most likely you have something else going on.

At the thermostat, if you turn the Fan to the ON position, does it work? How about if you turn the Heat ON? If either of those two things work, then the trouble is most likely in the wiring or furnace and not in the thermostat, and you need to get the company out to fix that.

Personally I'd call the company that installed the system. It is still under warranty for parts, but whether the labor is still under warranty depends on the labor guarantee provided by the installer.

beenthere 07-01-2012 05:21 AM

Look to see if it has a jumper between RH and RC. it should have one, if not that is most likely the problem. If it has one, make sure the yellow and green wires are connected at the furnace.

biggles 07-01-2012 07:03 AM

do you get FAN/On when you switch it on the stat?stupid question..sorry make sure the stat is in the cooling or auto mode..set all your temps the same if you have day modes like wake/leave/return/sleep that makes it a straight stat no bouncing of temps....set the actual time on the stat.... on the subbase do you have a wire coming up from the furnace landing on C if so then you have a constant 24V power there and the battery is back up.without C wire the battery is the power to run the board in the furnace. lets hear back on the C wire.shut the disconnect out at the condenser....wih the stat off subbase jump R to G should get inside furnace fan HI SPEED,remove jump them jump R to Y....go outside remove electrical cover on condenser unit contactor should be buzzing and or pulled in?NOTE: control power comes from the furnace /air handler out to the condenser....these are just simple DIY items you can check without a meter.....want to know about that C wire on the subbase...?to check freon remove the shrdder cap out on the insulated line into the the pin down with screw driver(like a car tire) just to burp some freon and let up...should be a healthy burp more then a car tire(don't worry it is only gas state not liquid)...i will tell you other stuff but lets get this general items you have a digital meter

designSTL 07-01-2012 02:59 PM

In response to your questions,
1. The fan does not work (nothing coming through vents at all) even though thermostat is set to on, I also tried in auto but still nothing
2. The thermostat is hardwired (terminal c is connected)
3. I selected 'hold' on the thermostat which overrides all previously set programming for temperature changes based on the time of day/day of week and selected my new setpoint temp, when I did this the snowflake icon next to current room temp begins to blink which my manual says is indicating compressor delay but even after the 5 minute delay has relapsed nothing kicks on. The fan symbol and snowflake symbol are both present which should mean they are on but they are not.
4. I do have a jumper wire between RH and RC
5. Furnace light switch is 'on' and every breaker has been reset

So before I disconnect out at the condenser, doesn't the fact that neither the fan nor heat work either likely mean the problem is inside somewhere?

designSTL 07-01-2012 03:00 PM

I do have a digital meter but am very unfamiliar with how it works.

scottmcd9999 07-02-2012 04:03 AM

You can try jumping out the thermostat - jump RC to Y and see if the outdoor unit comes on, then jump RC to G and see if the fan comes on. Note there could be a delay with the fan, if the furnace includes a Delay On timer for that fan. If jumping out the tstat resolves the issue, then replace the stat and you should be okay.

Otherwise, check the following:

1) Control fuse on the circuit board in the furnace (if there is a circuit board). It looks like a 3 or 5 amp automotive fuse, and you can get one from any auto parts store.
2) Power to the furnace - make sure that all panels are in place correctly. Newer furnaces have "kill switches" that can disconnect power to the system if the panels aren't replaced correctly.
3) Is there any auxiliarry drain pan beneath the furnace? If so, does it have water in it? Aux pans should not have water in them, and some have a float switch to detect this and shut off power.

Otherwise, you'll have to use your meter to determine if the system has (a) high voltage (115 volts coming INTO the furnace) and (b) control voltage (24 volts at the R and C terminals on the board). If you're not sure about using that meter, see if you can find an online resource for your specific meter to show how it's used. You're checking AC current, so be sure to set the meter to the proper range.

bobelectric 07-02-2012 08:44 AM


Originally Posted by designSTL (Post 955602)
I do have a digital meter but am very unfamiliar with how it works.

Stop right there and call a pro.

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