furnace questions

[siliconbauhaus]

Update

I looked at the unit just now and the burner's fire up but no fan. Whichever way the switch is set on the t'stat it doesn't come on.

Looking at the blower unit, it has 3 wires running from the furnace electrical panel to it and it has a small part that sits in a holder on the case that has a pair of wires running from inside the motor up to it. I'm assuming this thing is a capacitor but I have no idea if it's a replaceable part or not considering the age of the thing.

I might have a wander down to blowes and see if they even carry such a thing and check out if they carry blowers there as well.




I live in a 50's rancher. It's the typical sort of thing ie brick veneer, no insulation, aluminium windows and a hvac system from the 70's at a guess.

I know the hvac system is getting close to needing a replacement but right now it's band aids at the ready as I don't have 4k+ spare. The ac condenser has a small leak that we get by with having a company top up the freon. I know this is a bit naughty but you do what you can at the time.

Now that fall has arrived out of nowhere the ac worries are done with for the season but now I seem to have a issue with the furnace. The missus switched it one today and we got the smell of burning dust (I hope) but the blower on the furnace keeps pulsing rather than starting and running.

I changed the thermostat a month or so ago and then found out that despite wiring the thing as per the labels on the wires, it seems to be backwards. Auto = on and On = auto. I don't know if this is causing the pulsing on the furnace or not.

Anyone here with experience of furnace issues? I could certainly use some advice before having to call someone out and lose my arm and possible leg.

[Uncle Cracker]

What's a furnace??

[toolguy1000]

if your furnace dates from the 70's, don't wait to replace. it is way past it's useful life and the unfortunate thing about furnaces is that when they go bad and start emitting CO into the house, the occupants stop waking up in teh morning. i replaced fiurnaces in each of my first 2 homes and never regretted. even with a minimally efficient unit today, you will save money over what you are using now. you and whoever else lives there are worth the 4k.

[master53yoda]

is the furnace blower a belt drive or direct.

verify that the blower wheel turns ok.

Most belt drive motors have a start switch and the pulsing is what the do when the switch has failed.

Direct drive motors won't have the start switch but will have a run capacitor. these will pulse if the run capacitor has failed.

let us know what you find out. The pulsing shows that the controls are energizing the fan. do not let it sit and fire without the fan as you are overheating the heat exchanger, the high limit switch typically has a limited number of cycles before it fails.....

[chrisk]

$4k is mostly on the high end. I had a new 70k btu, 95% efficient furnace installed last year for $2,200 last fall, less than $2,000 with energy rebates through the gas provider. This included the permit, removal of the old system and a new direct vent system, plus a 10 year parts and labor warranty on the new one. Between the new furnace and new programmable thermostat, I bet we saved $500 last year over the old system running through the winter.

My only suggestion would be to shop around for a new furnace. Also, look into some of the energy rebates out there for insulating your home.

First things first, fix the wiring at the thermostat and see how that affects things.

[siliconbauhaus]

Thanks for the advice so far.

Unfortunately as far as replacement goes it's really out of the question right now as we're basically hand to mouth and keeping the mortgage paid is the main priority.

I pulled the fuse for the furnace to make sure no one tries to turn it on until I've had a chance to have a look at things. I'll have a look at the blower to see if it's a belt drive or not. I'm pretty mechanically inclined but I'm always wary of things plumbing /gas.

As far as the thermostat and the backwards wire it seemed to be fine with the ac running although we had to remember it was backwards. I'll swap the wires over this weekend.

[billwmeyer]

I usually have the burning dust smell every year when I turn on the furnace for the first time. I let it cycle once and usually the smell does not re-occur. If you keep smelling that odor, I would get it checked.

I have no idea about the pulsing fan. I do not see how the wires being switched would cause that.

Bill

[woodturner]

the unfortunate thing about furnaces is that when they go bad and start emitting CO into the house, the occupants stop waking up in teh morning.

CO detectors are HIGHLY RECOMMENDED for all homes with gas appliances or equipment. One common reason furnaces will emit CO is that the heat exchanger is cracked. Many furnaces have a 10 year or more warranty on the heat exchanger - so the repair might even be free.

[siliconbauhaus]

I have 2 CO alarms in the house. One downstairs near the water tank / furnace and the other up at the top of the stairs.

I did have the fuse pop at the board for the furnace so maybe the fan caused that and is in need of replacement. (I only just remembered about that)

[Mr__Bill]

You really should have the furnace serviced by someone familiar with that vintage furnace.

That said....

The smell could be dust burning off of the heat exchanger and fed by the blower. Try vacuuming it off with a shop vac. open the door where the filters are and you should see the blower, vac everything you can. Whatever you do don't try to vac out where the fire chamber is.

The pulsing, I assume you mean the fire. The furnace has a flame detector that needs to see fire for the furnace to keep running. This prevents a non lit furnace from continuing to put gas into the fire chamber and eventually blowing the house up. If the detector is dirty it can't see fire and the thing will pulse as it tries to start up. If you really know what you are doing you can pull the flame detector and wipe off the end and that may make it work, but the detector may be dead and need to be replaced.

When getting a service person tell then the make and age of the furnace and make sure they are familiar with working on it. Some new guy with a few years experience may just tell you to get a new furnace or sell you new innards when it can be fixed. If other people in the area have the same age houses someone may have a service person that knows about the furnace, ask around one of them may even know how to fix it.

Good luck

Bill,

[siliconbauhaus]

Cheers for the suggestions Bill. When I say "pulsing" it keeps kicking on like it's going to start and then does it all over again. I did lightly feel the vent pipe and it was hot so something was burning in there. Maybe it's just the blower trying to start up and failing.

I'll have to ask around the neighbourhood and see if I can find any of the older couple left around here and ask about a repairman. The couple of times we've had someone look at the ac condenser they immediately go into salesman mode and say we need a new system.

[charliex]

If it's not a motor problem.... I had a similar problem with a unit at my old house. Turns out the furnace didn't like the new electronic thermostat I had installed. I had to go back to the mechanical type.

Chas

[woodturner]

When I say "pulsing" it keeps kicking on like it's going to start and then does it all over again.

I've had that problem when the batteries in the electronic thermostat were getting weak but not weak enough to trigger the low battery indication. Might be worth changing the batteries if you have that type of thermostat.

[siliconbauhaus]

The unit takes batteries but I think it's only for the backlight part. I'll have to look at the manual to be sure. It replaced a previous digital thermostat and that didn't have any issues getting the fan to start.

[Mr__Bill]

If the fan works in AC mode then it's not the fan that has a problem in heating mode.


Bill, over here where my furnace sleeps in bed with me.....