Hello Everyone,
Well, just because life thinks I am made of money, our home ac isn’t working. It isn’t coming on in either the auto mode or when switched to fan on. I have checked the fuse panel and non of the fuses are tripped. The filter is clean and new so it isn’t frozen over. More than likely I will have to call out a professional to take a look at it, but prior to spending the money it will be worth asking if I am over looking something obvious. And yes, it is quite possible that the unit died, although last time I had a tech out here he found no problems and said everything looked good. The unit is about 10 years old I would assume. So, is there anything simple that I can check prior to calling a tech out?
Is there a switch either on the main unit, or nearby it in the house, that could be flipped off? I’ve see a couple units over the years that had a switch, for some reason, that would get accidentally turned off once in a while.
If the heat works, and things just aren’t happening when switching to a/c, then I got nuthin’.
A broken thermostat? I’ve seen them work fine in the heating mode and not at all in the cooling mode. Might be worth popping a new cheapy thermostat on to check. Also replace the batteries in the thermostat just in case.
Even if the breakers don’t looked tripped I would still make sure they are firmly seated in the panel and cycle them on and off on the off chance it’s a wonky breaker connection.
Also some AC units have a separate breaker panel right near the unit. Might be worth checking to see if you have one of these. Be careful as these are usually high amperage connections.
Ok - forgive me if these are stupid suggestions, but did you actually switch it from “heat” to “ac” (most cheap/ mid priced thermostats require this).
Also - I think - if you are testing the heat - and then switch to ac (if the heat was on) - it may have a limit to how fast it switches (supposed to save wear and tear on system I think). I think this can be minutes - so if you turned it - it didn’t work - and you turned it off - try being more patient
Ooops double post but does your ac use the furnace fan? If it does, and the fan works for the heat and not for the ac then look up that specific problem on the internet. That should be a helpful troubleshooting issue.
Is anything happening when you flip it to fan mode? All that should happen is that the main blower in the furnace should start running. If that’s not coming on it could be a few things. A power switch turned off, a bad blower, a bad board, bad t-stat etc…
As SeaDragon said, start by checking for a switch and make sure it’s on. If it’s on, you’ll need to make sure it’s getting power (on the furnace side of the switch). After that, I’d pull off the bottom panel and check the circuit board to see if the LED is blinking. If it is, you can look up the code, if not, I’d make sure the main blower was getting power (have the t-stat on FAN, hold down the safety switch and check the leads that feed the blower with a volt meter).
If the fan is coming on, you’ll want to make sure the compressor is getting power. If it is, you’ll probably need to call in a pro, things start to get a little dicey in there. Motors are harder to test (ya know, cuz of the big spinning fan blade on top), and if it’s not that it tend to be refrigerant related.
Ditto on checking the thermostat.
Thanks for the suggestions, at this point no luck. Nothing at all is happening, and I have checked the thermostat and even replaced the batteries in it with no luck I am thinking that it might possibly be the capacitor. This happened at our last home, the capacitor was bad and the unit was never able to get the power it needed to start. Not a cheap repair, but not a new unit either. Anyways, I have checked all I can reasonably check so I guess it is time to call a technician out tomorrow and get a professional diagnosis. Thanks for the help.
The cap on the main blower or the cap on the compressor? I’m still confused, does anything happen when you flip the t-stat to FAN?
If your main blower has a cap, you could check it yourself if you wanted to reach in there and spin up the motor by hand…
Also, screw you, I woke up with 4 inches of new snow in my driveway this morning.
My vote: compressor relay. If you don’t understand what this means, call a repair guy.
But if OP can’t get the main blower to come on by switching the t-stat to fan then the compressor isn’t playing into it. In that case the most likely culprit is no power to the furnace (which sends a lower voltage signal to the compressor relay).
Okay, new information. I found a “hidden” fuse panel outside below the power meter. One was marked AC and was blown. I reset it, but still the unit doesn’t come on. This leads me to suspect even more so that it is the capacitor, my reasoning being that with a bad capacitor the unit is trying to draw more power and blowing the fuse. Does this make sense?
A bad motor start capacitor should only affect the compressor. So, if nothing is working you have a problem farther up the line.
I’m not sure this is applicable, but I’ll toss it out there.
I had a similar problem with my old a/c unit. However unlike the OP, the blower DID come on, just not the compressor.
The way I resolved this a couple of years in a row was to set the thermostat to a low temp in a/c mode and flick the outside circuit breaker a couple of times - slowly, not up and down repeatedly.
Apparently during the off-season, the compressor would be “stuck” or “frozen” and flipping the switch was enough to nudge it back into operation.
Of course that should have been my cue to replace the outdoor unit, but oh no, I had to wait until it died. In retrospect, given the efficiency of the new unit, I probably would have been better off replacing it at the first sign of trouble. Understandably, that’s not always an option, especially these days.
I have a gas furnace and A/C that share duct work, controls and blower. Ok, what works and doesn’t work? If the blower comes on in fan on mode, the breaker for it, its relay, and the control voltage is getting to the thermostat. If nothing happens, as suggested, reset the breaker. Also, there is a small fuse on the control board.
If the blower comes on in A/C, but not the compressor, it could be the thermostat, compressor relay, compressor breaker, the fused disconnect outside by the compressor, the compressor, or any of the wiring and connections.
HVAC 101
Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. The thermostat is wired to switch the power from the red to the white, yellow, and green as needed with the blue completing the circuit. Most thermostats and furnaces have the contacts labeled R, B or C, W, Y, and G for the corresponding wire colors. Many have RH and RC to allow separate transformers for heating and cooling. With just one red wire, jumper them. It may be wired to have the A/C control wires return to the furnace and its controls and then a second wire goes to the A/C unit. Internal wiring may replace the green wire if the thermostat does not give you the option of fan only or continuous fan. Digital or programmable thermostats may need the blue wire connected to them.
To do simple checks like this you do need some tools. A test light, a meter, or a voltage detector might be the best place to start with. I came across the niftiest gadget for trouble shooting, a voltage detector. They work through the insulation of wires. There are several brands. I have a GB Instruments GVD-505A, less than $15 at Home Depot. Touch it to a hot wire, and the end glows red. Find the doodad that lights it on one side, and not the other, and you have the culprit. You do not have to open up housings and expose electrical contacts. You are looking at where your hand is, not where the meter is. Most people are capable of doing repairs and will get it going and not get hurt if they use a little sense. The voltage detector makes it even easier.
In A/C on mode, both the green and yellow wires should be connected to the red wire. If you have 240 and 24 volts to the relay inside the compressor housing, the relay may be bad. Often you can push the contacts together with something non conductive. If that starts the compressor, the relay is bad. A safe, easy thing to replace for anybody careful to shut the power off. That largely what the disconnect by the compressor is for. While mucking about with the wires, you can see that it is off.
It is probably not the thermostat.
Do this:
- Turn the heat on, and raise the set point to make a call for heat. Does it come on?
If yes, it’s not the transformer or power to your furnace, or the low voltage fuse on the circuit board.
If no, the problem is common to both the A/C and heat so it may be the circuit board, 115V power to the furnace (including the breaker), fuse on the circuit board, low voltage wiring or thermostat. (although probably not the thermostat)
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Turn on the fan switch. Does it come on? See above as the causes will be similar to item 1 above.
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Turn the A/C on and run the setpoint down to make a call for cooling. Does the fan inside come on? Does the outside unit come on?
If the indoor fan comes on, and the outdoor unit doesn’t, it’s a problem outside, and if so, the most common problem is the capacitor outside. It could also be the contactor, or the 240V fuses outside or the 240V breaker inside.
If neither the indoor fan or outdoor unit comes on, it could be the 115V power to the furnace, thermostat, low voltage fuse, low voltage wiring, or a couple other less likely things. Also check to make sure the panel on the furnace is on securely; there is a “door switch” that will disable the units if the door is ajar. (a common occurrence)
I’d be hesitant to go buy a new thermostat. While it may be the thermostat, most often it is not.
A bad capacitor will rarely blow a fuse. Rarely. It simply keeps the outdoor unit from coming on.
There may be a circuit breaker at the panel, and fuses at the disconnect. Check the fuses. If the breaker tripped, and the fuses are blown, they most often tripped for a reason.
If so, you may have a grounded compressor. That’s bad news.
Silly question…did you turn it all the way off and then all the way back on. Just flipping a breaker back to ON typically won’t reset it.
I see Raindog is here and he’s the guy to listen to, but IMO (and he touched on it) one of the most important questions is still going to be…when you flip the t-stat to fan, does the fan on your furnace spin up. Knowing this little piece of info is really going to go a long way in troubleshooting the problem. (Mainly because the answer may help to isolate the issue).
Also, I’d be curious to know the answer to this question after you reset the fuse again. It’s possible, you reset the fuse and then blew it again as soon as you tried to turn the AC back on. You might want to make sure everything is shut down before you reset it again.
Thanks to everyone for your suggestions. I had finally given up and called a AC repair company. They came out today and it turns out the problem was a internal fuse inside the air handler unit. It was on a rocker switch hidden in the back of the unit. So good news that it only cost a $89 service fee. I got off lucky as I was fearing the worse. Thanks again for the help.