Ask Me Help Desk - Central air cond air handler doesn't come on but compressor does.

Quote:

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.

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.

Quote:

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

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?

Quote:

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?

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"??

Quote:

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?

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

Quote:

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

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.

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

Attachment 10181

Quote:

Originally Posted by bstanley

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

The pic is posted.

Quote:

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.

The pic is posted.

Quote:

Originally Posted by bstanley

The pic is posted.

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

Quote:

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

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.

Quote:

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.

Hi Wally - You still here?

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

Quote:

Originally Posted by bstanley

Hi Wally - You still here?

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??

Quote:

Originally Posted by Joshdta

Did you ever get this fixed?????

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.

Quote:

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.

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.

2 Attachment(s)

Quote:

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.

[attach]Attachment 18411[/attach]

Quote:

Originally Posted by bstanley

[attach]Attachment 18411[/attach]

This is an on/off switch located in the attic on the outside of the air handler. One shot is the bottom of the switch and one is inside the switch. Unlike regular light switches, this has that black circular thing with the 2 light blue connectors on it.

Have you ever felt the fat motor to see if it was extreamly hot? Soory I am new to this question but would love to help. And that pic you just put up looks like some sort of limit

Sounds to me like the cooling fan relay is going, or has gone bad.

Quote:

Originally Posted by Joshdta

sounds to me like the cooling fan relay is going, or has gone bad.

But why would the cooling fan relay work when the temperature in the attic is cooler. Is this fan relay heat sensitive? It seems that once the blower is going, it keeps going.

If it's too hot in the attic, and I flip on the air, the outside condenser comes on, but the air handler doesn't. I replaced the capacitor on the blower already and that wasn't it. I've been told that relays either work or they don't. Are limit switches heat sensitive?

As I said, if I turn on the central air in the morning before I go to work... before the sun heats up the attic, the air handler & outside condenser will run fine for days. For instance, if I turn on the central air now and turn it cool enough so that it comes on, I'll have no problems because there isn't any heat in the attic yet.

Quote:

Originally Posted by WallyHelps

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

Wally, I posted the picsfof that switch and the limit type device under it. Could the heat affect this? It almost would make sense. If power doesn't flow through this switch, obviously no power to the blower.

The limit switch should have no purpose during the cooling cycle.

Also I am a Factory York dealer so if you airhandler is york let me see what I can come up with.

I Should be back on this afternoon and let you know what I found.

Ok so far the control board you have there is acctually called a electric heat control. So there may be something on it locking you out. Your t-stat wires do not connect to this control do they? Also I would like to know where the two wires coming out of that little black switch conect to.

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Quote:

Originally Posted by Joshdta

Ok so far the control board you have there is acctually called a electric heat control. So there may be something on it locking you out. your t-stat wires do not connect to this control do they? Also i would like to know where the two wires comming out of that little black switch conect to.

Josh - Yes it's a York around 10-11 years old. I don't think the t-stat wires are in or attached to this switch but I'll have to go up and check as I haven't been up there since last August. I'm attaching a pic of all 3 components on the outside of the air handler. I tried to get the circuit board from some of the local vendors but nobody seemed to have it and most wouldn't deal with me because I'm not a plumber. I did replace the capacitor as that was the most obvious culprit but that wasn't it. The silver square piece hanging down is the face plate of the on/off switch.

Attachment 18424

Quote:

Originally Posted by Joshdta

also i am a Factory York dealer so if you airhandler is york let me see what i can come up with.

Josh is going to be a MUCH better resource than I will be. I am simply a very handy (retired engineer) homeowner. I defer to an expert. :o

Quote:

Originally Posted by WallyHelps

Josh is going to be a MUCH better resource than I will be. I am simply a very handy (retired engineer) homeowner. I defer to an expert. :o

Thanks Wally... I appreciate your help.

You say all these controls in the pic are outside of the unit? I am trying to find out just what exactly that little black switch is so far no luck. But still looking

These intermitant problems are always the toughest to figure out.

Quote:

Originally Posted by Joshdta

you say all these controls in the pic are outside of the unit? i am tring to find out just what exactly that little black switch is so far no luck. but still looking

Yes. I say outside, but I had to take off the cover on the right side of the air handler. This revealed the components you see in the picture. As far as I can tell, this light switch looking switch has to be there so a tech can shut the power off before servicing the unit? My thoughts are to bypass this switch. Tie the power directly to the unit so this switch isn't in the picture. Of course, I won't know if this is successful until the temperature in the attic get's hotter.

Would the outside condenser have anything to do with this? A few years back, a capacitor went in this unit. The air handler continued to operate but blew warm air because the outside unit wasn't operational. It was rather obvious that the capacitor was shot because it looked liked a M-80 went off in it. I replaced that and all was OK.

Nothing on the out door unit would cause your airhandler to shut off. The light switch you speak of should be just a on and of switch. So you do not get shocked will working on the unit. So I do not think the light switch is the problem. You have 2 relays 1 built into the transformer, and a fan really that is the black one built onto the circuit board. When you say to get it to run and cool your house all day do you mean by turning the ac on early and turning it way down to like 65 or so? Or do you mean you turn the fan switch from auto to the on position? I know you attic is probably not hot enough right now for anything to happen. But when it does warm up. Try just turning the fan to the on position and leaving the t-stat set at normal 72 or where ever you keep it. If it stays cool and works like that then it is a 90% chance the problem is in the transformer really.

Quote:

Originally Posted by Joshdta

Nothing on the out door unit would cause your airhandler to shut off. the light switch you speek of should be just a on and of switch. so you do not get shocked will working on the unit. so i do not think the light switch is the problem. you have 2 relays 1 built into the transformer, and a fan realy that is the black one built onto the circuit board. When you say to get it to run and cool your house all day do you mean by turning the ac on early and turning it way down to like 65 or so? or do you mean you turn the fan switch from auto to the on position? I know you attic is probally not hot enough right now for anything to happen. but when it does warm up. try just turning the fan to the on position and leaving the t-stat set at normal 72 or where ever you keep it. If it stays cool and works like that then it is a 90% chance the problem is in the transformer realy.

The t-stat is digital. Honeywell (I replaced that too by the way). On the left side of the display is Auto & On... 2 selections. On the right, heat & cool. We have baseboard heat, so the heat selection obviously doesn't get used.

We use to set the air to auto, cool and set the temp to 70 in the morning when the attic was cool. That worked for several years. Last year however, what would happen is the temp would reach the 70 and the air would turn off. Once the temp went above the est point the outside unit would come on, but not the air handler. This created a fairly decent flood into the insulation and stained the ceiling above where the air handler is. So then what I did was turn the control to "on" but not set it to "cool". The air handler would come on but not the outside unit. I would do this around 6:30 AM. When my wife got home from work at 4:00 PM the air handler would still be running but the house would be up above 80 because the t-stat was not set to cool. She would then go t-stat and set the control to cool but leave the left side at "on" not "auto". Upon doing so, the outside unit would come on and proceed to cool the house.

As I had mentioned, during a heat wave last year, we left it in the above configuration for at least a week straight. Because the unit was set to "on" and not "auto" it wouldn't shut off if it hit the selected temp. If for some reason it shut off, and I tried to turn it back on, the outside unit would come on, but no air handler until the attic cooled.

So what ever the problem is with the air handler, it's heat related.

By the way, I've had the pro's out twice to look at it and both concluded there's nothing wrong and I must be nuts, because there's no thermistor's or any thing like that in the air handler that would not work intermittlently due to heat.

Last year I took that transformer to several HVAC places but they either didn't have it, or wouldn't sell it to me because I'm not a licensed plumber.

One of the guys at a HVAC joint said that it couldn't be the transformer because they either work, or they don't. Heat wouldn't have any effect on it. I told him a beg to differ and basically he told me I'm a stupid home owner that shouldn't be in their store.

A regular transformer does either work or it doesn't, but you have a trransformer/relay combo. Well as I was saying if it runs fine on the fan on setting, with the cool on. But not the auto setting with the cool on. Then the relay at the transormer is getting hot and not kicking in. What happens is when there is a call for heat the t-stat will send power to your outdoor unit. Thus the outdoor unit comes on. But the t-state does not send power to the blower. That is why the really kicks in to tell the fan to come on. When you have turned it to the on position you have bypased that really and it works good. So from what I am thinking. The stupid home owner as you said had it figured out last year and the people at the heating company are really the stupid ones. What state are you located?

I think Josh is leading you in the right direction. Nothing I can add here. Good luck and please let us know what he final outcome is.

If you are deadset on doing this yourself, it may be a matter of replacing parts until problem is fixed. I hate to do it that way, but sometimes you just have to do it. I would start with Joshes advice(replace trans, relay). Its your best bet at this point.

Quote:

Originally Posted by Joshdta

A regular transformer does either work or it doesn't, but you have a trransformer/relay combo. well as i was saying if it runs fine on the fan on setting, with the cool on. but not the auto setting with the cool on. then the relay at the transormer is getting hot and not kicking in. What happens is when there is a call for heat the t-stat will send power to your outdoor unit. thus the outdoor unit comes on. But the t-state does not send power to the blower. that is why the realy kicks in to tell the fan to come on. when you have turned it to the on position you have bypased that realy and it works good. So from what i am thinking. The stupid home owner as you said had it figured out last year and the people at the heating company are really the stupid ones. what state are you located?

I'm in South Windsor, CT. 10 minutes norteast of Hartford. Any suggestions as to where I might get my hands on this transformer/relay combo?