A/C electrical problem


Periodically, about 2-3 times a year, I notice an error code on our thermostat, E2, which indicates a problem with the 24 v. power to it. But before I can even do anything, within an hour or so, it's always resolved itself. It's out again now, but this time I noticed that it coincided (I imagine) with a power "issue". I now recognize that since I have a UPS on my computers now, and heard it click. However, no outage occurred in the rest of the house, so I imagine it was a spike. Anyway, I've re-set the circuit (though it wasn't tripped) that gives power to it, and it still says E2. Any thoughts on what it could be, or what normally happens that has resolved itself in the past?
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A couple additional points: after shutting off the breaker and then turning it back on, it goes to resumes to a seemingly normal state where it says the current temp, which is of course higher than the set one. And then at the point where I imagine it would kick in, instead of saying 83, it goes to E2 and gives the error message. So it's apparently when it's about to kcik in. Oh, and guess what? It just kicked in! LOL.. Any thoughts?
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You first need to know what the definition of an E2 error code is. If your UPS chirped you probably had a dip in voltage. If the line voltage to the transformer powering the thermostat is lowered, the secondary voltage, which should be 24 volts, will decrease as well. Possibly the thermostat is just notifying you of that fact, then when the voltage is normal, it resets.
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The E2 says a problem with the 24 v. power, nothing more specific. I don't KNOW that it's linked to the outages. In fact, I now recall that in the past it, at least sometimes, occurred while I was getting a message that the filter needed changing. So then I thought it was the pressure/resistance (know it's not correct technically) was causing it. Well, today we came home with a new filter, and it was like that, but I was changing it when it kicked on (I think after I powered it off and then on), but regardless, I put the new filter in, and it clicked off again. I wasn't home when this initially shut off this time. I just know that we've had a lot of power drops lately. Now, it's kicking in (I can here it "trigger" at the thermostat), but then 1-2 minutes later, I imagine when it's meant to actually send air (the air handler is meant to kick in?), it shuts off and gives the E2 error again. So, fwiw, it appears that the thermostat is working in that it acknowledges the temp is above the set temp, it sends a signal to start the air conditioner, the compressor kicks in and charges the system?(Okay, I have no idea if that terminology is right!:) and then when the signal is sent to the air handler to blow the cooled air through it shuts off again? Does that sound like what's happening? If so, or not, any suggesitons? Thanks much!
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Isn't this fun! Yet more info! Okay, now it switched from E2 to the current temp, and it occurred to me to switch the fan from Auto to always On. So I did, and the Fan did kick on for about 10 seconds. And then the E2 came up again. But I'm ALMOST sure that in the past the fan hadn't yet kicked in when it occurred, though I could be wrong. If so, would that point to a problem between the thermostat and the air handler, or condenser and air handler, but only when the fan is going to kick on automatically when the A/C is on, but that the signal is fine from the thermostat to the air handler to tell it to turn on now?
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I don't have enough info about the thermostat or the A/C system to determine. Typical system will have a transformer in the blower unit that controls both the relay in the outside condensing unit and the inside blower unit. When you switch the stat to cool, it should send 24 volts to both inside and outside units simultaneously and continuously until the room temperature is satisfied. You may have a weak or undersized transformer
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We've always had a lag time between hearing the thermostat "click" and the air start to blow. Sorry for getting the specs to you all late: Our system is a Carrier FV4ANF005 The condensing unit is: can't read it and get a hit on google. A couple years ago, probably 3, I had to replace the blower motor, and do recall that it was a variable motor - reportedly a big waste of money, but that's what the original ower had been sold on, and what I was told I had to replace it with. The entire system was put in about 10 years ago. Aside from the blower motor, I"ve had to replace/have replaced the contactor in the condensing unit every year or two. As far as I know, everything else is OEM. The thermostat is a Carrier Auto Changeover one. I don't have a model number, just reading off of some online documentation I once tracked down, that based on the photo is what we have. ... ooh, I just looked at doc's that I had found online for our thermostat, and it specifically says at the end of them that an E2 reading means that there is not enough voltage for the system to operate. Nothing new, really, but confimation that it's not enough?
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So, something is causing the voltage to decrease on the transformer. Could be any number of things from loose connection to a bad transformer. You need to hang a meter on the transformer and see what happens when the loads are applied... or call for service
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fortunately, I have a trusted (if he's still alive) A/C guy, and 1 day before we go on vacation for 2 weeks! Thanks again!
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Okay, another big DUH... I can't even recall the symptoms when the contactor went out. Could it be that?!
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It's possible. If the contactor is bad, the condenser won't start. Keep in mind that the condenser may have a timing circuit in it to prevent it from short cycling
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didn't occur to me right away... Jeez... Anyway, I cleaned off the contacts and got it working for the night. It appears to have been the contactor, which I'll replace tomorrow. THanks much. BTW: I'm guessing that that explains the E2/low 24 v. code? Obviously, if there's NONE, it's low. Would it also be the cause of intermittent E2's? I hadn't noticed them increasing in frequency, as one (I imagine) would expect.
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albee wrote:

The low voltage could be caused by the wrong tap connected on the input of the low voltage transformer. If it's a heat pump, the air handler may be fed by a 208-240vac circuit and the 24 volt transformer may be the type with a primary winding for that voltage range. The transformer will have two different primary winding taps, one for 208 and one for 240. Low voltage feeding the coil of a contactor will keep it from closing forcefully enough which will cause the contacts to arc and burn. You would notice a loud buzzing sound from the contactor when the coil is powered.
[8~{} Uncle Monster
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On Wed, 30 Jul 2008 03:06:30 -0500, Uncle Monster

correctly that 208v could be feeding the 240v winding tap of the transformer, causing the quick burnouts of them? When I first encountered this (changing the contactor yearly) it was suggested that the a/c must be cycling on and off too quickly, though I didn't know why it would. So I guess this would be an alternate explanation? Re: the buzzing, would it be a momentary one, just as it's powered, or would it stay on? I haven't noticed it, but then, haven't listened for it, either. Thanks much!
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albee wrote:

Well, check it out and let us know. I hope you have a means to check your voltage and current. You can pick up inexpensive test equipment from a Harbor Freight store if you have one in your area. The big box stores and Radio Shack have a more expensive selection.
http://search.harborfreight.com/cpisearch/web/search.do?keyword=multi+meter&Submit=Go
http://tinyurl.com/5phvcx
[8~{} Uncle Monster
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On Wed, 30 Jul 2008 16:54:48 -0500, Uncle Monster

Thanks; I do have a multimeter. Not completely sure how to USE it, but I have it :) Unfortunately, I'm getting ready to away for 2 weeks, so don't have a bunch of time. Didn't want to ask a stupid question like where is my transformer. So, for now, I used some steel wool on the contacts and got it working temporarily, and then went to get a new contactor today. But I have another question: He started to give me a contactor that looked the same, but upon inspection I found had different specs. Could that be the cause of the low voltage? Since the contactor has been switched out a few times, and once by an A/C guy who hooked it up wrong! and they had to come out to re-do it, so it's possible that they didn't replace it with the right one. I have one in my hand which could be the one I just had on that failed, or the one from a year ago, and the one that I just bought, both have these specs on them (the 180 under LRA could be 160; so small!):
24 VAC
VAC FLA LRA RES 240/277 40 240 50 480     40 200 50 600 40 180 50
Now, I looked at the one I have on it right now, which could be the one that failed or one that had quickly failed a year ago (either way, the same performance), but that I cleaned up and is running it now, has these specs. I THINK this is the one that was on most recently, because it has a cover, of sorts, over it, which I think they've added more recently.
40A Definite Purpose Contact 24 VAC 120 VAC 240 VAC
VAC FLA LRA RES 277 40     240 480 32 200 60 or 80 600 25 160
Now, the one they started to give me at the parts store, the best that I can recall, had FLA ratings of 30 and RES ratings of 40. The guy said that this was the max, so that this one, (which is the same as I had on it) was better. Would any of these specs cause there to be too much resistance, and hence a weaker voltage and the problem? I have a feeling I'm setting myself up for a comment along the lines of, "Quick, call someone who knows something!", but thought I'd ask. :)
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