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Originally Posted by Missouri Bound

NO. The fan switch on the thermostat is just a control. There will be a contactor of some sort that the fan switch controls in the air handler. On my heat pump, for example the fan would continue to run after the air conditioner was satisfied. It turned out to be a fan switch (relay) which was sticking. After replacing it the switch worked normally. And some furnaces have a fan control which sensed heat rise after a burner fires up and starts the fan and allows it to run after the furnace flame kicks off to circulate and to cool the heat exchanger.

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Misso - The Air Handler is a York Model # N4AHD14A06A Serial # EDFS098644 - unit supply 208/230 volts 60 hz. Again, it's cool only. We have baseboard heat. I'd say that it's 10 years old or so. We've been in this house 8 years. The former owner had this installed a few years prior to us buying this house. There's also a number up on the right side of the tag LR49182C. So right now, 8:30 AM, I've put the fan on, and it's running fine because the attic isn't hot at this time. After it gets a little hotter today, I'll click on the cool and the central air will work fine even though the attic will be sweltering. If I turn it off mid day and then try to turn it back on... no dice, the air handler won't come on but the outside compressor will run?? Question... a transformer either works or it doesn't? Ther's no it works sometimes and sometimes not... yes? This is what one of the supply house workers told me. He didn't think it was the transformer because it works in the morning.

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Originally Posted by WallyHelps

I'll jump in here...
My guess is that this switch is just for safety. You can kill power to the blower so it would be safe to stick your hands in there. I would seriously doubt this would contribute to the problem, but while you're replacing things it would be a cheap experiment. Just kill power at the breaker beforehand!

WallyH

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So... strange but true. I turned the fan to "on" Saturday morning just to make sure the air handler would go on. I didn't set the control to "cool" until around 11:30. It's been running like that with no problem since Saturday morning and still Monday evening. The outside compressor cycles on and off when it hits the set temperature but the air handler stays on obviously because I have it set to on instead of auto. However, if I turn the air off this evening and try to turn it back on tomorrow afternoon when the attic is hot... butkus! No air handler.

I can't find any schematics for your air handler. But maybe you can answer this... when you open up the service panel of the unit, is there a circuit board which the thermostat wiring connects to, or are there various components the stat wiring is directed to? Does the switch on the thermostat ALWAYS turn on the fan when placed in the on position? Does the fan start immediately when in the auto position and the thermostat calls for cool? If the fan relay is good, perhaps... and it's a strong perhaps that you have a voltage problem... any chance you can check the voltage at the fan relay, and at the thermostat?

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Originally Posted by Missouri Bound

I can't find any schematics for your air handler. But maybe you can answer this.....when you open up the service panel of the unit, is there a circuit board which the thermostat wiring connects to, or are there various components the stat wiring is directed to? Does the switch on the thermostat ALWAYS turn on the fan when placed in the on position? Does the fan start immediately when in the auto position and the thermostat calls for cool? If the fan relay is good, perhaps...and it's a strong perhaps that you have a voltage problem....any chance you can check the voltage at the fan relay, and at the thermostat?

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Main power goes to a regular on off switch. Then white & black go to the transformer. Also at the bottom of this on-off switch is a small circular type thing with two connectors on it. I think it might be a limit switch type thing? The T-Stat wires, green & red connect to the transformer (yellow isn't connected and electric taped with a loop at the end, so as not to expose the end of the wire... cool only) Then from the transformer, there are 2 wires that connect to a smaller circuit board that has a little black box on it. I was going to replace this transformer but apparently it's a special part that I would have to get from York directly. I've been told however that either the transformer works or it doesn't. There's no in between. Do you agree with that?

The fan will start immediately in either "on" or "auto" when cool is pushed... if the attic isn't to hot. Once the attic reaches a certain temperature, the fan doesn't go on. No sound or anything, just no fan. For instance... on Saturday, I turned the fan to "on" early in the morning because we were having a party and I wanted to make sure that we had the central air working. I didn't set the t-stat to cool however. The fan came right on with no problem. I left it on then around 1:00 with the attic already sweltering, I clicked on the cool. The outside compressor came on and because the blower was already going, magic we had central air. I let it run like this until this morning when the humidity and heat finally cleared out. The compressor cycled on & off all week but the only difference was I left the blower to "on"??

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Originally Posted by bstanley

Main power goes to a regular on off switch. Then white & black go to the transformer. Also at the bottom of this on-off switch is a small circular type thing with two connectors on it. I think it might be a limit switch type thing?? The T-Stat wires, green & red connect to the transformer (yellow isn't connected and electric taped with a loop at the end, so as not to expose the end of the wire...cool only) Then from the transformer, there are 2 wires that connect to a smaller circuit board that has a little black box on it. I was going to replace this transformer but apparently its a special part that I would have to get from York directly. I've been told however that either the transformer works or it doesn't. There's no in between. Do you agree with that?

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Can we get a photo of that round thingy? (and the circuit board, if you're taking pics anyway).
I agree that it would be unlikely that a transformer would have a temperature sensitivity, so I'd put that on the back burner for now. I'd concentrate on any electronic items that are subject to the attic heat.

We won't let this stump us!
WallyH

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Originally Posted by WallyHelps

Can we get a photo of that round thingy? (and the circuit board, if you're taking pics anyway).
I agree that it would be unlikely that a transformer would have a temperature sensitivity, so I'd put that on the back burner for now. I'd concentrate on any electronic items that are subject to the attic heat.

We won't let this stump us!
WallyH

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Absolutely... I'll go up there this weekend and get the pics!

I suspect that the "little black box" is probably a fan relay, unless you have one mounted somewhere else in the unit. And I suspect that if the board has the fan relay on it, you probably will need to replace the board.

Pictures will help and any numbers available on any parts would help as well.

Wally - Here's the pic of the board with the potential relay on it.

Attachment 10181

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Originally Posted by bstanley

Absolutely... I'll go up there this weekend and get the pics!

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The pic is posted.

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Originally Posted by Missouri Bound

I suspect that the "little black box" is probably a fan relay, unless you have one mounted somewhere else in the unit. And I suspect that if the board has the fan relay on it, you probably will need to replace the board.

Pictures will help and any numbers available on any parts would help as well.

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The pic is posted.

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Originally Posted by bstanley

The pic is posted.

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Sorry for the delayed reply... I just got back from vacation (7/16-7/22).
That does look like a relay, and I could believe that a component like that would be more susceptible to heat than the other resistors, capacitors, etc. Unfortunately, you can't be certain without swapping it out--which probably requires a whole new (unreturnable) circuit board.

Earlier you mentioned a round thing. Did you happen to get a photo of that too? I'm guessing that is some type of thermal switch/fuse, and might be suspect.

I sure hope it isn't as hot where you are as it is where I was!
WallyH

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Originally Posted by WallyHelps

Sorry for the delayed reply...I just got back from vacation (7/16-7/22).
That does look like a relay, and I could believe that a component like that would be more susceptible to heat than the other resistors, capacitors, etc. Unfortunately, you can't be certain without swapping it out--which probably requires a whole new (unreturnable) circuit board.

Earlier you mentioned a round thing. Did you happen to get a photo of that too? I'm guessing that is some type of thermal switch/fuse, and might be suspect.

I sure hope it isn't as hot where you are as it is where I was!
WallyH

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Hi Wally - I hoped you enjoyed your vacation. Yes, it was pretty darn hot up there. Crud, I can't believe I forgot to take a pic of the thermal switch thing. I forget where I saw it, but it looked allot like a limit switch... I think. I'll get up there again this weekend and get a pic of it. By the way, the air has been on for a week straight now without any problems. As I had mentioned, I have to keep the fan in the "on" position however instead of auto.

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Originally Posted by bstanley

Hi Wally - I hoped you enjoyed your vacation. Yes, it was pretty darn hot up there. Crud, I can't belive I forgot to take a pic of the thermal switch thing. I forget where I saw it, but it looked allot like a limit switch...I think. I'll get up there again this weekend and get a pic of it. By the way, the air has been on for a week straight now without any problems. As I had mentioned, I have to keep the fan in the "on" position however instead of auto.

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Hi Wally - You still here?

TIS PROBLEM WAS 8 MONTHS AGO,, surely it has been fixed by now

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Originally Posted by bstanley

Hi Wally - You still here?

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I am still monitoring this problem... and hope you have indeed found the problem. This has been quite a mystery, and I'd like to know the resolution for my own information.

WallyH

What you can do is when the fan kills out. Turn the power of and feel the back of the motor. If the motor is to hot to touch then you need a new motor, if it is relatively cool. The odds are it is the fan relay on your circuit board.

Did you ever get this fixed??

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Originally Posted by Joshdta

Did you ever get this fixed?????

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No, not fixed. I'm going to attach a pic of a switch that is on the air handler that has a black circular resistor type thing that has two wires on it. Maybe someone can tell me what that is. Last year, we lived with the fact that we had to turn the air on in the morning before it got hot in the attic. I'd like to fix it this year however. Stayed tuned while I try to remember how to attach a picture here.

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Originally Posted by Joshdta

What you can do is when the fan kills out. Turn the power of and feel the back of the motor. if the motor is to hot to touch then you need a new motor, if it is relatively cool. The odds are it is the fan relay on your circuit board.

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Here in lies the problem. Once the airhandler is on, it will run until I turn it off. Just as long as it goes on before the sun starts to heat up the attic. Last summer I was able to turn on "fan only" around 6:30AM. Then when I got home from work, I clicked on the air portion and everything is cool. At one point, it ran for almost a week straight because of a heat spell. If I tried to turn it on when I got home from work however, no dice, the outside condenser comes on, but not the air handler.

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Originally Posted by bstanley

no, not fixed. I'm going to attach a pic of a switch that is on the air handler that has a black circular resistor type thing that has two wires on it. Maybe someone can tell me what that is. Last year, we lived with the fact that we had to turn the air on in the morning before it got hot in the attic. I'd like to fix it this year however. Stayed tuned while i try to remember how to attach a picture here.

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[attach]Attachment 18411[/attach]