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The Swamp
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Home A/C Air Handler

Mon Nov 06, 2017 9:35 am

I saw a thread on here about home maintenance, and I thought some of you might have some experience with a problem I am having.

My home a/c air handler blower is flaky. It will come on sometimes when I turn on the unit. Other times, only the outside compressor will come on and the blower will remain off. The blower motor, which is up in the attic, will usually come on if I go into the attic and wiggle one of the unit kill switches. I have a float switch for the condensation pan that kills power to the unit if the pan fills with water. I can wiggle that up and down and the fan will usually kick on. It will stay on sometimes for a while, sometimes just for a few minutes before I have to wiggle the float switch again. I changed the float switch, believing that to be the problem, but it did not solve the problem. When it's running, the fan seems to be working normally. It's just getting it to fire up, or stay on for the full cooling period, that's the issue. It also displays the same issue during a heating cycle too, so it's solely a fan issue.

Could the problem be a dying fan relay? Perhaps the board on the blower is going bad? The unit is about 14 years old. Anyone have any ideas what this might be? Thanks!
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Re: Home A/C Air Handler

Mon Nov 06, 2017 9:57 am

I'm assuming these switches are low-voltage. Given the location you list, I'm betting that the LV contacts are corroded and not making good contact. This could go all the way to the LV contacts in the relay. If you can see the contacts in the switches, a quick hit with some 600-grit sandpaper until they're shiny again should get you going. Otherwise, I'd replace all of the switches/relays on the LV side of things.
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The Swamp
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Re: Home A/C Air Handler

Mon Nov 06, 2017 10:12 am

I checked all of the connections and they seemed good. I know a flaky relay can cause problems, or the board itself might be on the blink. I've never had any issues with the air handler before, and I'm hoping it's something easy to replace if possible.
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Re: Home A/C Air Handler

Mon Nov 06, 2017 5:47 pm

At fourteen years old, it's possible the motor bearings are getting dry, or maybe the start & run capacitors are baked out, or possibly the brush contactors are worn down. Have you disconnected power and then checked the motor for proper lubrication and excessive play? Have you inspected the brush contactors? Have you tried replacing the capacitors?
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Re: Home A/C Air Handler

Mon Nov 06, 2017 7:18 pm

Fairly common cause of blower motor and condenser fan motors failing to spin up is the capacitor. Super cheap to replace and easy to check. Most meters have a capacitor test function.
 
The Swamp
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Re: Home A/C Air Handler

Mon Nov 06, 2017 7:30 pm

It's strange because I can jiggle the float switch or cycle the panel cover kill switch and make the fan spin up again.

That's why I'm wondering if it's maybe a relay that's going out, and the power cycle energizes it enough to make the fan restart? There are two diagnostic LEDs on the control board, and it's not giving an error condition, so I think the board is okay. It's just the fan that keeps stopping. Sometimes I don't have to do anything and the fan will spin up again. I don't know what's making it stop, though, mid-cooling.
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Re: Home A/C Air Handler

Mon Nov 06, 2017 7:45 pm

StefanVonS wrote:
Fairly common cause of blower motor and condenser fan motors failing to spin up is the capacitor. Super cheap to replace and easy to check. Most meters have a capacitor test function.


I've had this happen twice. Both times the A/C compressor fan's hub got really hot without being able to spin the fan.
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Re: Home A/C Air Handler

Mon Nov 06, 2017 8:33 pm

If it is spontaneously stopping, then I'm less inclined to think it is the capacitor. Sounds like you may be on to it with suspecting the relay. When the fan is stopped, can you check voltage to the fan at the board? See if you can get a universal control board to replace it with. If it solves the problem, then money well spent. If it doesn't, you can return it. Most HVAC supply houses should have something in stock you can use.
 
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Re: Home A/C Air Handler

Mon Nov 06, 2017 8:52 pm

The Swamp wrote:
It's strange because I can jiggle the float switch or cycle the panel cover kill switch and make the fan spin up again. That's why I'm wondering if it's maybe a relay that's going out, and the power cycle energizes it enough to make the fan restart?

Could be. Could also be the system is stalling for some other reason, and the relay cycling gives it a quick kick that sometimes convinces it to start.

In theory, fan motors ought to be reliable enough but the Amana in our HVAC died in less than ten and blew out a relay contact at the control board for good measure. And just to be spiteful, Amana (though now owned by Whirlpool) uses a special bracket that is incompatible with the universal replacement motor that fits most other brands.
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Re: Home A/C Air Handler

Mon Nov 06, 2017 9:45 pm

ludi wrote:
In theory, fan motors ought to be reliable enough but the Amana in our HVAC died in less than ten and blew out a relay contact at the control board for good measure. And just to be spiteful, Amana (though now owned by Whirlpool) uses a special bracket that is incompatible with the universal replacement motor that fits most other brands.

Huh, motor in our Amana died young too. Fortunately the repair guy had an adapter bracket in his truck.
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The Swamp
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Re: Home A/C Air Handler

Tue Nov 07, 2017 9:15 am

When I was up in the attic this morning trying to get the fan to kick on, as I was wiggling the kill switch, I could hear something quietly clicking and the fan trying to start up. Finally, after a few tries, it did.

So, relay?
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Re: Home A/C Air Handler

Tue Nov 07, 2017 9:20 am

The Swamp wrote:
When I was up in the attic this morning trying to get the fan to kick on, as I was wiggling the kill switch, I could hear something quietly clicking and the fan trying to start up. Finally, after a few tries, it did.

So, relay?

Is the relay up there with the fan, or somewhere else with the control panel?
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Re: Home A/C Air Handler

Tue Nov 07, 2017 9:31 am

Captain Ned wrote:
The Swamp wrote:
When I was up in the attic this morning trying to get the fan to kick on, as I was wiggling the kill switch, I could hear something quietly clicking and the fan trying to start up. Finally, after a few tries, it did.

So, relay?

Is the relay up there with the fan, or somewhere else with the control panel?


I'm not sure. I didn't see one near the main board, but I suspect it's near the blower. Maybe attached to the blower itself. I am guessing the clicking is the relay trying to engage, but not quite being able to, if that sounds right.
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Re: Home A/C Air Handler

Tue Nov 07, 2017 9:35 am

The Swamp wrote:
I'm not sure. I didn't see one near the main board, but I suspect it's near the blower. Maybe attached to the blower itself. I am guessing the clicking is the relay trying to engage, but not quite being able to, if that sounds right.

It does sound like the relay is the issue. The low-voltage side isn't latching down (thus the rattling/clicking) so the high-voltage/current side of the relay can't get juice to the fan. The next question is if the failure to latch the LV side is in the relay itself or in the associated LV wiring/sense switches.
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Re: Home A/C Air Handler

Tue Nov 07, 2017 10:34 am

Captain Ned wrote:
The Swamp wrote:
I'm not sure. I didn't see one near the main board, but I suspect it's near the blower. Maybe attached to the blower itself. I am guessing the clicking is the relay trying to engage, but not quite being able to, if that sounds right.

It does sound like the relay is the issue. The low-voltage side isn't latching down (thus the rattling/clicking) so the high-voltage/current side of the relay can't get juice to the fan. The next question is if the failure to latch the LV side is in the relay itself or in the associated LV wiring/sense switches.


I replaced the float switch, so I know the problem is not there. There could be a problem with the panel kill switch I suppose. How long do relays typically last? The one I have now is 14 years old. When they begin to die, do they display these kinds of symptoms?
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Re: Home A/C Air Handler

Tue Nov 07, 2017 10:38 am

Dirty or worn relay contacts could cause that sort of behavior.
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Re: Home A/C Air Handler

Tue Nov 07, 2017 10:42 am

The Swamp wrote:
How long do relays typically last? The one I have now is 14 years old. When they begin to die, do they display these kinds of symptoms?

In a system like yours where the relay trips all year-round, it's probably old and tired. Failure to latch the LV side is a common failure symptom, but you'd be well-advised to check continuity to all of your LV switches (cheap multimeter, hold switch closed, check continuity at wires coming into control panel) before jumping right to the relay.

Something like this is all you need.
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Re: Home A/C Air Handler

Tue Nov 07, 2017 10:54 am

FYI, spraying a (unpowered of course) connection with white vinegar will easily dissolve any of that white DC electrical corrosion. Just a little trick my dad always used for his boat trailer.

White vinegar is a miracle cleaning fluid.
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The Swamp
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Re: Home A/C Air Handler

Tue Nov 07, 2017 12:28 pm

I need to locate the relay in the unit so I can get a part number from it. Relays don't seem to be particularly expensive, so even if that's not the ultimate cause of the issue, it will help to rule it out. But, in my experience, the relay does seem to be the most likely culprit. A few days ago, I was actually unable to shut the blower off. The blower was not responding to the thermostat switch. That's also a sign of a relay going bad. Lennox units seem to have separate relays that are not a part of the controller board, so that's good. Replacing the board is spendy.
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Re: Home A/C Air Handler

Tue Nov 07, 2017 7:39 pm

My model number for the Lennox unit is G50UH-36A-070.

I was unable to locate anything inside the unit near the blower that looks like a relay. I wonder if the relay is on the control board made by White-Rodgers. I've heard some relays are on the board itself, which means the board will have to be replaced if the relay goes out. I've reached the limits of my Google Foo. Anyone have any ideas?

I did find the capacitor, though. It's the original capacitor, so it's 14 years old, too. I know a dead capacitor will prevent the motor from spinning up. Could a dying capacitor cause the problems I'm seeing?
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Re: Home A/C Air Handler

Tue Nov 07, 2017 11:12 pm

The Swamp wrote:
I was unable to locate anything inside the unit near the blower that looks like a relay. I wonder if the relay is on the control board made by White-Rodgers. I've heard some relays are on the board itself, which means the board will have to be replaced if the relay goes out. I've reached the limits of my Google Foo. Anyone have any ideas?

For modern, consumer-grade HVAC all relays are typically on the control board, unless you have a combo gas/heat-pump unit, in which case there's often an additional interface board and relay interposed between the thermostat, the heatpump, and the furnace. Unless you can locate an exact replacement relay set (try Mouser or Allied Electronics) and have excellent soldering skills, a control board replacement is likely required.

I did find the capacitor, though. It's the original capacitor, so it's 14 years old, too. I know a dead capacitor will prevent the motor from spinning up. Could a dying capacitor cause the problems I'm seeing?

Some of the symptoms, sure, although the wouldn't-shut-down thing is more likely a control issue.
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The Swamp
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Re: Home A/C Air Handler

Wed Nov 08, 2017 9:27 am

I had a feeling the relay might be incorporated into the board. It's clever to design it that way, given that it allows Lennox to charge $200 when a $6 part goes south.

I'll start with the low hanging fruit for the moment though, and replace the capacitor. I know a cap going bad can cause all sorts of problems spinning up the fan, and the cap I have is very old. So, it's a reasonable guess that my issues might be related to a dying cap. If that doesn't fix it, then I guess I'm headed to the board room.
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Re: Home A/C Air Handler

Wed Nov 08, 2017 10:46 am

I talked to a friend of mine who is a Lennox dealer, and he confirmed that the relay is on the board itself. Ugh. And he told me to get 14 years out of that board was pretty good. He also said he thinks it's the relay. I'll pick up a cap anyway since they are cheap and the one in there likely needs replacing anyway. Ah well, so my new computer purchase is, once again, postponed.
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Re: Home A/C Air Handler

Wed Nov 08, 2017 12:57 pm

Bust out the soldering iron and replace the one that's on the board?
 
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Re: Home A/C Air Handler

Wed Nov 08, 2017 1:17 pm

I wish! My solder skills are not quite up there with Brew's, I'm sorry to say. It looks like I can order a new board online for about $130, so that's not too bad. Everything looks plug and play. As long as everything mostly matches up, it shouldn't be too complicated. A new cap is only about $10, so I'll pick one up today and install it. Then move on to the board if the problem is still there, which I expect it to be.
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ludi
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Re: Home A/C Air Handler

Wed Nov 08, 2017 1:44 pm

Unfortunately these boards are made to be replaced, not repaired. The connector swapping is correspondingly easy. Repairing, especially around relays, is often tedious because of high-current traces and cheap substrates.
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The Swamp
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Re: Home A/C Air Handler

Wed Nov 08, 2017 11:15 pm

I got the wrong cap. The parts list shows I need a 5 something, but the cap in there now is a 7.5. I assume that's a big deal?
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ludi
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Re: Home A/C Air Handler

Thu Nov 09, 2017 12:41 am

The Swamp wrote:
I got the wrong cap. The parts list shows I need a 5 something, but the cap in there now is a 7.5. I assume that's a big deal?

Like-in-kind is the best bet although most DC electrolytic and AC motor-start capacitors are accurate to only +/- 20%. In any case, the motor will have slightly less starting torque than what it was designed for, although it may be enough. I assume you ended up with something like this?
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Re: Home A/C Air Handler

Thu Nov 09, 2017 1:51 am

Capacitors and 32Vac transformers are subject to failure from power problems/ damage at any time.
 
The Swamp
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Re: Home A/C Air Handler

Thu Nov 09, 2017 7:59 pm

I picked up the correct cap this afternoon and installed it when I got home.

The a/c blower powered right up, and has been functioning normally. It's already gone through a cooling cycle, turning on and off as set by the thermostat. I'm guessing the old cap was out of range and wasn't able to kick start the blower motor. When it did, it wasn't strong enough to keep it running.

As always, you guys rock. Thanks for the help!
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