quick fact check on fan - furance/thermostat

[micky]

My neighbor, who is quite a jerk**, is having trouble with his Carrier oil furnace. He says the furnace goes on and off but the fan stays on all the time. He says the thermostat is in the auto position, not On.

Looking at the wiring diagram, it seems clear to me that the fan is controlled by the G and Y terminals on the control box, which is controlled by the G and Y terminals on the thermostat. Which are probably connected by green and yellow wires. And maybe (unlikely) the thermostat is bad, or stray wires from the G or Y are touching the other terminal. And at the very least disconnecting one of those two wires will stop the fan or not, and give essential debugging information . (And reconnnecting it right after, because the fan is needed when the burner is burning. I'm talking about the warm air house circulation fan, not the fan that blows air into the oil burner.)

Also, and this I'm less sure of, the fan can stay on for months without stopping and without burning out without shortening its life much. So being on 24/day for a few days didn't hurt the fan, but might have cost him a little money.

I don't need any help on this afaik,since I've spent plenty of time on an identical furnace.... unless I said something incorrect above. Did I?

**If I hadnt' had bad experiences with him, I'd print out the wiring diagrams of the furnace etc. and take it with me tomorrow evening, but he's been such a pain. He never identifies himself when he calls. Last winter when I went over and couldn't fix it, I asked him when he got it fixed to find out what the problem was and let me know. He didn't do that. I asked him to call me when the paid repairman is there. He didn't do that.

But the prize was when he wanted an oil pump, and I have spare parts for many things because when a neighbor got a new furnace, I got the old burner. So it was the day of the funeral of one of my best friends (and he knew that), my first good friend to die, under depressing circumstances, and after I got home from the funeral, instead of going to sleep like I wanted to, I took the time to take the oil pump out of the burner, clean up the dripping oil, wrap it up and put it on the porch, as I told him the night before I would do. He never came to pick it up, he never called to tell me I could put it back in the house, he never called at all, and he never thanked me. Nothin'.

Since then I've brushed him off a couple times, and I wouldn't even go tomorrow except I'm curious and he lives less than 100 yards away.

I'm especially curious because he told me that pros told him the control box needed replacing. (He called me 3 or 4 days ago to get my spare control box but a) I used it already, b) he told me the problem and I told him the control box has nothing to do with it.) He gave me the name of the company that told him that and their webpage says they've been in business since 1983. That's a long time to not understand what controls the fan. His business address seems to be his home, and he has a biggg home, 2 2/2's or 3 1/2 high, with a biggg swimming pool, and a tennis court, a 3-acre lot backed by acres of woods, neatly trimmed bushes and neatly mown lawn, in an expensive suburban n'hood not so far away. He couldn't screw up that often, so this must be some shlock employee giving out bad advice.

[Iggy]

replying to micky, Iggy wrote: Not that I'm even a novice, but is there a separate board or controller for this unit's blower fan? I haven't seen such a thing before. If not, then I'd have to agree with the HVAC guy and/or his employee. Or, do you think he screwed with it or that even the HVAC Company set it up to swindle him during a previous "friendly" service call? Or, is this just really old wiring that has cracked or unfurled insulation (really-really old)?

[gfretwell]

You really need to find out more about how this is wired. Some old "heat only" systems only used 2 wires and the fan control was in the furnace.

[micky]

There are one two connection screws on the outside edge of the board for the furnace control box. But they aren just there for convenience and aren't connected to anything in the control box.

I don't think so, but I think he might be in over his head. Maybe a guy who went along on calls with someone who knew what he was doing, and is doing this outside of working hours, but still using the name of his employer.

When I look up the company name it says HVAC/R (what's R? Oh, refrigeration) and seems to emphasize the control aspect of it, which of course is just what my friend needs. But when I put the address of the business in google maps, it deduces that there is a business there and in the sidebar, it says Dry Wall Contractor. That's a far cry from what he needs.

The company seems to do a variety of things (which is why he has such a nice house): Infrastructure Improvements, Operations & Maintenance (O&M) Construction Management Dedicated Project Managerment.

Probably not. My insulation isn't cracked and his wasnt' when I looked at it last year. But your question reminds me that they didn't use stranded wire, of course. So I don't think it's a stray wire. And the two screws are over an inch from each other.

So it's more likely it's the auto/on switch on the thermostat. If it were my house, I'd disassemble the thermostat and try to fix the switch, and if that didn't work, I'd put in an external SPDT switch, connected by a short 3-conductor wire. I have lots of switches, but I'm not willing to do all that for him, and I'll let him buy a new thermostat. But I don't know if he can put it in, as simple as it is. I don't like dealing with people who can't do anything.

[micky]

It's wired like mine, heat and AC. The whole house is like mine, or the mirror image of mine.

I'll try to let you all know what it turned out to be.

Thanks to both of you.

[trader_4]

How bizarre. The guy is an AH, you're going to go over there anyway, but because he's an AH you're not going to take wiring diagrams with you?

He never identifies himself when he calls. Last

I see nothing but trouble here. I'd just stay away. The blower could very well be stuck on because of a bad controller, which was what was diagnosed. Or like Gfre said, very old furnaces just used thermostatic switches in the furnace plenum to turn the blower on and off.

[Iggy]

replying to micky, Iggy wrote: I found a couple of videos that might actually double-check what you're doing and should be helpful in getting this guy out of your life. The 1st is about the Blower Running and gives great information on the Thermostat's fitness and then also the wiring and board causes and workarounds...Blower Fan Motor Won't Shut off!- STEP by STEP Troubleshooting!

The 2nd is about the different generations of Fan Limiter switches. If you have the first of biggest type that has the silver disk, there's a white button or knob on the bottom left that needs to be pulled or set to the outward position for Auto Fan operation or the Fan Limiter needs replacement if the Auto setting doesn't kill the fan...Why is my fan running all the time with no heat

[micky]

Curiosity has me.

I wasn't, but my memory for stuff like that is bad, and the page was right in front of me, so I printed it.

There is no controller, only a relay. Disconnecting the relay coil would be the next step. Its the black and blue wires, connected to the G and C terminals respectively.

No, he was told the problem was what he called when he talked to me "the grey box" (which I then called the control box). Or at least that's what he wanted to get from me. I once found my exact box on the web and I think it was under 100, but a furnace repair company would probably charge 200 or more. If they had actually told him it was the relay, $45 plus 50 labor, I think he would have done it. It's the 2 hundred dollars plus what, 50 - 200 labor** that's making him balk. If I remember, I'll ask him how much they wanted.

The relay otoh would cost $20 as a relay and maybe 45 as a furnace part and I think the fan relay enclosure is right on the face of the furnace, chest high and easy to get to, but I don't have the exact part and I'm not going to do it.

I know for sure he said they said it was the control box, and I know for sure, that's not the problem.

**I wish there was a webpage that rated furnace repairs, like there is for auto repairs.

Not in the plenum, in the thermostat.

[makolber]

no in the furnace .

the air handler blower in my furnace can be turned on 2 different ways.

1) by the wires in the thermostat which you already discussed 2) by a bi metallic switch in the furnace

the cycle goes like this

1) thermostat calls for heat this turns on the burner AND the blower 2) furnace heats up the house 3) thermostat stops calling for heat this switches off the burner and the blower BUT..... 4) the blower keeps running because the bi metallic switch in the furnace is still warm this keeps the blower running until the heat in the furnace has been removed.

the bi metallic switch in my case also is the hi limit and will turn off the burner if the temp in the furnace gets too high.

there are two tabs that can be adjusted

If the blower tab is adjusted too low, the blower will never turn off.

it is something like this

mark

[makolber]

and this

mark

[trader_4]

No, like Gfre said in the plenum. Even in newer installs where there is a fan wire, that wire doesn't turn the fan on and off when the furnace fires up. The furnace does that itself. The fan switch on the thermostat is there only to allow you to turn the fan on that way as an additional way. It's extremely unlikely the thermostat switch would fail in the closed position. Short in the wiring is possible, but unlikely. My bet would be a controller problem at the furnace, which is what the repair service diagnosed.

Also, not that it matters, you said that it doesn't cost too much to run the blower full time. That's true if it's one of the new ECM motors, they do use less electricity because they are more efficient and because they run it at very low speed to circulate the air. But if it's an older furnace with a PSC motor, it will use a lot more because it's not as efficient and it will run faster than one of the new ones because it thinks it's running for heat, not the slow speed typical to just recirculate.

[trader_4]

Agree with you on the overall process, with one exception. The furnaces like this that I have seen, the thermostat doesn't turn on the blower and the fan. It only turns on the burner. The temp switch that you describe then turns on the blower after the temp in the plenum has risen to a set point, which takes a min or two from burner start.

And if he has one of these, it could be as simple as the plenum switch needs adjusting. Or it could be the tech is telling the truth and it's a furnace with a controller that's kaput. Given that Micky says the neighbor is an AH, I wouldn't get involved as all I see is trouble.

[micky]

Even if you're right, yes and no. He gave my neighbor N the impression that it was the grey controller box, and the limit and the fan and limit switch is elsewhere. not in something that is called a controller. So either the pro was wrong, or he doesn't communicate well, or he did get it right and say it right and Neighbor still got it wrong.

I said it "might have cost him a little money". I was not ignoring the money aspect, but not trying to guess how much.

The motors are 3 speed but once the wires are connected, they stay at the same speed all the time. Mine was set on low, probably his too, but I don't think that is as low as new blower motors go during the cool-down phase, or maybe even the always on phase. So it definitely cost him money, and he doesn't have that much, but not my problem.

Thanks for insisting on what you meant, even when I didn't get it.

[micky]

Oh, I get it. I know about this but in my defense, I was confused by the word "just", which must have applied to a different part of the idea.

I know about it, but I hadn't thought about it, so I'm glad I posted. In fact, this is exactly the sort of thing I thought I might have missed.

I asked him, twice, if it worked right when he last got it repaired but he mumbles and I couldn't tell what he said.

Thanks for both links. The video is good. It's amazing to me that a bimetal strip can make so many cycles and still work. I don't actually know my limit switch is working but I know the furnace stays on about the same amount of time as it always has after the fire goes out.

i've also never seen a strip that big/long. I guess I just didn't think about what was inside the thing.

Here's a website where the guy has printed advice on HVAC and he says if you write to him, he'll give personal advice. What could be better than that? Well, he doesn't mention charging but maybe he does. It would be fair.

And of course he said he got home at 4 but it's 5:40 and he hasn't called and might not ever. But I wasn't holding my breath.

But this is still good for me, because I won't forget about this switch again.

As I said, I intend to tell you all how this ends up.

[micky]

Thanks. I may just send this to my neighbor!

And maybe the links in the other posts too.

I must say that for homeownershub, you are at the top.

[Iggy]

replying to micky, Iggy wrote: You're welcome. I hope it resolves maybe even the relationship.

[trader_4]

That's true for sure if it's a very old furnace. IDK exactly when they moved away from the temp switches and went to other control methods. Do you know for sure what it has or doesn't have? I would think furnaces even 20+ years ago could rely on a controller as part of what makes turns the fan on and off.

So

Maybe, but you haven't convinced me, or even gone over there to figure out what's wrong, have you?

They probably stay at the one speed for heating, but if they have AC, AC typically is higher speed.

Any time.

[micky]

Yes. I forgot that the fan and limit switch could keep the fan on, but I didn't forget it existed.

It's 38 years old.

He was supposed to call a little after 4 and now it's 9!

But I know what he said and that's enough to know what's in my previous paragraph.Because he asked me for the grey box and there is no chance the problem is in the grey box. (Starting "So either....wrong."

Nope. Same speed for heat and cooling. You have a new model.

Except the wiring diagram I downloaded shows the default to be running at high speed until the burner or AC shuts down and then low speed until the fan switch cools down. I'm not positive that part corresponds to what's here. I remember only two of the fan motor wires connected to anything, but I looked 30 years ago and might not have been paying attention even then. At any rate, MY fan didn't run at high speed ever, but at low speed of 3 or 4 speeds. (Because I switched the wires to make the fan quieter, trying every choice, and it was already as quiet as it would get. The colors indicated that before I started, but I tried anyhow.When that didn't work I started closing my bedroom door.)

Somewhere I have the paper manual that actually came with the furnace. I'm not sure it wouldn't have the same discrepancy, but if I remember I'll check, when I find it.

[trader_4]

Probably time for a new one. I saw my bills cut in half going from one that was 25 years old to a new one. That was gas, with oil, the fuel cost savings in dollars is more substantial and they payback time would be reasonable.

[makolber]

that is EXACTLY the way mine operates the blower runs a low speed during the cool down.

its hard to tell one blower speed from the other by ear, but if you can, it would be a clue as to why the blower is on all the time.

Does it speed up when you switch the T stat from auto to On?

m