[bstanley]

If I don't turn the central air on in the morning, when the attic is cooler, the air handler won't come on but the compressor outside fires up. At night when the attic cools down, the air handler will work. I have replaced the T-Stat but that didn't help. Today, I put the fan on first, and it came on. I then hit the cool button and the compressor outside came on and all is fine. Previously, with the fan on auto, I hit the cool button and the compressor outside came on but no blower in the attic. Is there something in the air handler that senses heat?

[WallyHelps]

My first guess is to take a look at the capacitor on your blower motor. If this goes bad, your motor may not start reliably.
The ambient temperature may affect the characteristics of the capacitor enough to allow the motor to start when conditions are favorable.

There is, unfortunately, no good way to test capacitors besides swapping in a known good one.

This post shows one success story.

Good luck,
WallyH

[bstanley]

My first guess is to take a look at the capacitor on your blower motor. If this goes bad, your motor may not start reliably.
The ambient temperature may affect the characteristics of the capacitor enough to allow the motor to start when conditions are favorable.

There is, unfortunately, no good way to test capacitors besides swapping in a known good one.

This post shows one success story.

Good luck,
WallyH

Thanks WallyH - I know what the capacitor looks like on the outside compressor unit (I watched a tech replace it a few years ago) Will the capacitor look similar on the blower unit? I'm handy enough that I would attempt to replace myself.

[WallyHelps]

Thanks WallyH - I know what the capacitor looks like on the outside compressor unit (I watched a tech replace it a few years ago) Will the capacitor look similar on the blower unit? I'm handy enough that I would attempt to replace myself.

Yes, it will be very similar. Usually it is mounted to the blower assembly itself. Hopefully, what you'll find is it is swollen or something obvious.

Make sure you get an exact replacement (although you can get one with a higher voltage rating if you have to). Also, there is the possibility of voltage still present on the capacitor even with the power removed, so use insulated needle-nose pliers to pull the wires off the terminals.

Let me know how it goes.
WallyH

[bstanley]

Yes, it will be very similar. Usually it is mounted to the blower assembly itself. Hopefully, what you'll find is it is swollen or something obvious.

Make sure you get an exact replacement (although you can get one with a higher voltage rating if you have to). Also, there is the possibility of voltage still present on the capacitor even with the power removed, so use insulated needle-nose pliers to pull the wires off the terminals.

Let me know how it goes.
WallyH

Wally - Thanks for the heads up on the capacitor. I got shocked a few years back from a capacitor. I didn't get badly hurt but it scared the you know what out of me. It melted the tip of my screw driver to a screw.

What's odd about this situation is once the air handler starts blowing air, its good until I turn it off. For instance it started today as I had mentioned after I put the fan to "on" instead of "auto" and then clicked the cool button. It's been running fine all day. Even after it hits it's target tempature, it will clycle on and off (if it was on auto of course)although the attice is blazing. It's after it's been off for a while that the trouble starts with the heat in the attice and the blower not going on.

[WallyHelps]

That is odd behavior. And I've been known to come up with theories to explain something to fit in with a pre-conceived notion, so it is not a certainty that the cap is the problem. I happened to have extras lying around, so it was easy for me to swap in a different cap to test with. I know that most people don't have this luxury.

Best of luck,
WallyH

[bstanley]

That is odd behavior. And I've been known to come up with theories to explain something to fit in with a pre-conceived notion, so it is not a certainty that the cap is the problem. I happened to have extras lying around, so it was easy for me to swap in a different cap to test with. I know that most people don't have this luxury.

Best of luck,
WallyH

Well all was going well with running the air with the fan set to the "on" position then a few minutes ago, the blower cut out but the compressor outside kept running. I'm going to venture up there after this 100 degree weather stops to see what's what. Is there an access panel of sorts that will house the capacitor and other connections like the T-stat wires from the hall way?

[bstanley]

Well all was going well with running the air with the fan set to the "on" position then a few minutes ago, the blower cut out but the compressor outside kept running. I'm going to venture up there after this 100 degree weather stops to see whats what. Is there an access panel of sorts that will house the capacitor and other connections like the T-stat wires from the hall way?

So after the fan kicked off, I clicked the switch to auto, left the fan off for 10 minutes
And clicked the fan back to the on position and now its working.. weird.

[leddfoot]

Two things. First you can check if a capacitor is good if you have a voltage meter that has capacitance. It is signified as UF or a line with an arrow in it. Turn the power off to the air handler. Then discharge the capacitor (short the two terminals with insulated pliers or a screwdriver). Then remove one lead and read the two terminals. It should read at least 7.5 but the rating is on the side of the capacitor.

THE bigger question is does the air handler have a float switch in the drip pan. If the pan is full it will kill your ac, but it shuts the whole system down including the outside condenser so that system will not be able to remove any more humidity.

There is a panel usually on the side to access tstat wires, blower motor, and capacitor usually mounted on the blower motor. But shut it down (power), usually controlled by a lightswitch or disconnect, and open the panel nearest where your wires run in.

[bstanley]

Two things. First you can check if a capacitor is good if you have a voltage meter that has capacitance. It is signified as UF or a line with an arrow in it. Turn the power off to the air handler. Then discharge the capacitor (short the two terminals with insulated pliers or a screwdriver). Then remove one lead and read the two terminals. It should read at least 7.5 but the rating is on the side of the capacitor.

THE bigger question is does the air handler have a float switch in the drip pan. If the pan is full it will kill your ac, but it shuts the whole system down including the outside condenser so that system will not be able to remove any more humidity.

There is a panel usually on the side to access tstat wires, blower motor, and capacitor usually mounted on the blower motor. But shut it down (power), usually controlled by a lightswitch or disconnect, and open the panel nearest where your wires run in.

Leddfoot - There is a drip pan under the unit but it's not used. The system is set up with a pipe that runs from the unit to the outside about 20 feet of pipe. It looks to be about 5/8 cooper pipe. The condensation then drips to the outside. The problem is always with the blower in the attic, never the condenser outside however. I do have a sperry meter that measure voltage and ohms. I'll try testing the voltage. So far tonight, the fan in the attic cut out 3 times while the condenser outside kept running. After setting the cool setting to off, and waiting about 10 minutes, I turn the fan back on and click on the cool button and everything works. So far its been running fine on the "auto" fan setting which yesterday it wouldn't come on unless it was set to "on"... weird.

[leddfoot]

Ok the drip pan under the unit if it seems unused and you are running ac then it is a backup pan and there will be one inside under the evaporator coil where the copper pipes run into the air handler. Check for a float there although again, usually a full float pan will kill the call to the outside condenser. The copper pipe is actually the freon lines to that run to the outside condenser. Also (with the power off) in your air handler, try to spin the blower fins on your evaporator fin. A last note, the evaporator fan is typically but not always controlled by the green lead of your thermostat. You can check the call if you clip on the common side (meter on voltage) of the low voltage and find where the green lead returns to the air handler from the thermostat. However, note, this is a "hot check", don't do if uncomfortable with voltage, and if your air handler may have a door switch that kills all power when you open it.

[WallyHelps]

Leddfoot - There is a drip pan under the unit but it's not used. The system is set up with a pipe that runs from the unit to the outside about 20 feet of pipe. It looks to be about 5/8 cooper pipe. The condensation then drips to the outside. The problem is always with the blower in the attic, never the condenser outside however. I do have a sperry meter that measure voltage and ohms. I'll try testing the voltage. So far tonight, the fan in the attic cut out 3 times while the condenser outside kept running. After setting the cool setting to off, and waiting about 10 minutes, I turn the fan back on and click on the cool button and everything works. So far its been running fine on the "auto" fan setting which yesterday it wouldn't come on unless it was set to "on"... weird.

If the fan cuts out while running, I'd be less inclined to suspect the capacitor (but it could still be a problem--there are motor run capacitors). Also, measuring the voltage won't tell you much. Capacitance is a hard thing to measure (which is why the best test is swapping in a good cap). I suppose if the blower is getting really hot, it may cut out for thermal reasons (there is a thermal cutout).

All furnaces are a little different, but there should be a panel that you can remove to expose the blower. If you're lucky, it will be set up to slide straight out, revealing the motor and capacitor, etc. Or, even better, have the capacitor right out in the open like this.

Best of luck,
WallyH

[leddfoot]

Once again, capacitance is easily tested if your meter has capacitance. Turn power off, make sure power is off, dischage capacitor with insulated pliers or screwdriver (short terminals to each other and to ground(case)). It should typically read greater than 7.5 uf but the exact rating should be printed on the side. Of course, you have to have a meter that read capacitance and it is simple. Capacitance is the symbol to the right of the ohm symbol at this link. Fluke 187/189 Digital/Analog Multimeter. A capacitor diminishes as it fails and when it reaches the edge it gets intermittent.

[WallyHelps]

Once again, capacitance is easily tested if your meter has capacitance. Turn power off, make sure power is off, dischage capacitor with insulated pliers or screwdriver (short terminals to each other and to ground(case)). It should typically read greater than 7.5 uf but the exact rating should be printed on the side. Of course, you have to have a meter that read capacitance and it is simple. Capacitance is the symbol to the right of the ohm symbol at this link. Fluke 187/189 Digital/Analog Multimeter. A capacitor diminishes as it fails and when it reaches the edge it gets intermittent.

I do agree that it is easy enough to measure capacitance if you have the right equipment.
However, I think the normal homeowner/handyman in general does not have a meter that can measure capacitance. These are more specialized items that are not as common.

WallyH

[bstanley]

Ok the drip pan under the unit if it seems unused and you are running ac then it is a backup pan and there will be one inside under the evaporator coil where the copper pipes run into the air handler. Check for a float there although again, usually a full float pan will kill the call to the outside condenser. The copper pipe is actually the freon lines to that run to the outside condenser. Also (with the power off) in your air handler, try to spin the blower fins on your evaporator fin. A last note, the evaporator fan is typically but not always controlled by the green lead of your thermostat. You can check the call if you clip on the common side (meter on voltage) of the low voltage and find where the green lead returns to the air handler from the thermostat. However, note, this is a "hot check", don't do if uncomfortable with voltage, and if your air handler may have a door switch that kills all power when you open it.

Leddfoot - Actually the cooper pipe does lead to the outside as a drainage. There are also the freon lines coming in from the outside condenser. As a side note, I have base board heat. The central air unit isn't at all involved with the furnace. I have the outside compressor and the air handler... a rather massive looking unit is suspended from the joist's in the attic. So far today it was running fine and about 5 minutes ago... around the hottest time of the day, the blower kicked out again and this time isn't going back on... so says my wife.

[bstanley]

If the fan cuts out while running, I'd be less inclined to suspect the capacitor (but it could still be a problem--there are motor run capacitors). Also, measuring the voltage won't tell you much. Capacitance is a hard thing to measure (which is why the best test is swapping in a good cap). I suppose if the blower is getting really hot, it may cut out for thermal reasons (there is a thermal cutout).

All furnaces are a little different, but there should be a panel that you can remove to expose the blower. If you're lucky, it will be set up to slide straight out, revealing the motor and capacitor, etc. Or, even better, have the capacitor right out in the open like this.

Best of luck,
WallyH

Wally - I have baseboard heat. The furnace isn't involved with the central air unit. I have a compressor outside (York) and the air handler is in the attic suspended from the joists. It's a huge brown box with the ducts running out of it. Is there a thermal sensor in this type of air handler in the attic? If so, that would seem to me to be the obvious issue.

[bstanley]

Wally - I have baseboard heat. The furnance isn't involved with the central air unit. I have a compressor outside (York) and the air handler is in the attic suspended from the joists. It's a huge brown box with the ducts running out of it. Is there a thermal sensor in this type of air handler in the attic? If so, that would seem to me to be the obvious issue.

So it appears what ever the problem is has become permanent. The air handler fan cut out today around 4:30 and it's not going back on at all. We're expecting some strong storms tonight and relief from the 100 degree tempature luckily. I'm going to go up in the attic this weekend and remove the run capacitor to get a replacement. I'll let you know if that works.

[WallyHelps]

Wally - I have baseboard heat. The furnance isn't involved with the central air unit. I have a compressor outside (York) and the air handler is in the attic suspended from the joists. It's a huge brown box with the ducts running out of it. Is there a thermal sensor in this type of air handler in the attic? If so, that would seem to me to be the obvious issue.

I'm not familiar with this type of unit, but I would think that any modern motor would have a thermal cutout either on it, or close to it. If it is external, it should be in line with the power wires to the motor.

Good luck up there!
WallyH

[poorboy2]

Wally Helps sounds as if he has hit the nail on the head> Seems to me the "internal" overload is tripping off inside the evap motor. The cause could be the cap. Or dirty blower wheel that helps cool the motor's windings,

The motor and capactor both should be replaced now because the overload is so week or burned and the overload is inside of the motor be sure to put in a new cap. Of the right MFD and voltage

I know this is a fairly big job, it shoud be done by an A/C tech. To avoid this problem in the future change filter more often if the blower wheel is real dirty.

[bstanley]

I'm not familiar with this type of unit, but I would think that any modern motor would have a thermal cutout either on it, or close to it. If it is external, it should be in line with the power wires to the motor.

Good luck up there!
WallyH

I appreciate your help. I learned/learning allot on this site. So I did some testing these last 2 days after the heat wave. Here's the deal. This has been going on for 2 years now. If we didn't turn the central air on in the morning, we would have to wait until the attic fan cooled the attic enough at night, then the blower would come on. For the last 2 days, if I turn the blower on in the morning when the attic is cool, the blower goes on no problem. If I try turning the blower on around 5:00 PM or so, it doesn't go on. So definitely there's something in the blower that senses it's too hot in the attic and doesn't allow the blower to turn on. I believe that I was told about the run capacitor in the blower, is there a start capacitor as well in this blower? I haven't gone up there yet to look in the blower.