Forced air heater troubles.

billwhetzell

I am by no means an expert on heaters but probably have a better understanding than most ordinary people. We have an older trane forced air heater, about two months ago it quit heating, called the local heating company to come take a look. He works on it for about 10 minutes comes in and says easy fix 2 out of 3 of the open fuse links were bad and I replaced them and now your good to go. No explanation on why or anything, but we had no reason to doubt him as we had heat for the moment. Fast forward two months to yesterday, one new blower motor, 2 new breakers 10 open fuse links and we still have 0 heat. This system has ran great for 20 years practically maintenance free and all of the sudden after many failed attempts to fix the problem the heating company says the current ductwork is not adequate enough and we need to add a fresh air inlet, and they were going to tie it into the existing return air inlet duct before it enters the furnace, so the overall inlet air duct is the same size with just a different place to draw from. Isn’t that like adding more sand to an hour glass hoping it will flow more? I’m starting to feel like this is an attempt to only cool down the air enough so it quits popping the thermal fuses. We already have a $$ bill on the counter for the work they have done in the last two months and we still have no heat, and now they want to add the cold air system in. I’ve read on here that just putting in new fuses like that and walking away is most likely never going to fix the real issue, I’m looking for absolutely any insight on what the problem could be. They have inspected with cameras the existing duct work and said there are no blockages. Thanks!

hcpatel78

Check Control board...those are notorious to go bad...

JUGHNE

Sounds like an oversized electric furnace with inadequate air flow.
I have come across these a few times. They work when new and then either some elements fail or fuse limits open. They continue to heat because maybe 2 of the 4 to 6 elements still work. When one more fails then cold house.

Not only air flow issues but control problems.
I have disconnected half of the elements on some units and there is still adequate heat.

Other items could be plugged inside AC coil, dirty blower wheel, etc. Also have pulled pieces of insulation debris out of elements that was blocking air flow. All the air must have to pass thru a 12 x 12" or so square box where the elements are, so air flow is critical. Sometimes some of the air gets bypassed around that box somehow.

Rich_L

One should never just replace blown fuses and walk away. You need to figure out what caused it. That's sometimes easier said than done. I also agree with you that if the existing duct work was OK for the past 20 years, if there were no changes, it should still be good. There should be a temperature limit in the system to shut things down before fuses would blow. You didn't say but I'm assuming this is electric heat? If so has anyone pulled the resistance heater portion out and examined the elements?

billwhetzell

JUGHNE, if it is a 12x12 ish hole all the air needs to go through wouldn’t an 10x24 inlet be adequate to supply the air? I know there are some equations that go into figuring this kind of stuff out, or if that is considered pressurized air since it’s going through a reduced space. I’m just trying to grasp the concept of needing to add more air. We do live right next to the ocean so inputting salt air into a dry system sounds crazy. There is a laundry room behind the furnace that could be easily ducted too so it could still be a complete return air system and adding more air by returning it to the opposite side of the furnace from the current return where it would still be behind the filter.

billwhetzell

> @Rich_L said:
> It is an electric system, oldie but a goodie as all the techs have mentioned. The second time the fuses went the tech replaced the blower motor and said he visually checked and cleaned all components. Don’t know if that means he got his meter out and checked the limit switches, transformer or relays.

JUGHNE

No one mentioned your air filter.....I would assume it is a given that your techs have checked it out.
"An oldie" electric furnace has control components inside and often if the furnace overheats those components get cooked.
Also the wiring to controls can overheat and end up with loose connections which in turn add to overheating.
Fuse holders can lose their temper in the brass clips that hold them and overheat, which will overheat the fuse itself and so on.....the snowballing effect.

Do you know how much your furnace is rated for in KW?
It may be on the nameplate, but installer is supposed to mark the KW installed on nameplate.....but might not happen.

How many and what size of circuit breakers feed this thing?
Could you post a picture of the control panel.....may be behind a door held in place by 2-4 screws?

So you have AC?

pecmsg

Unfortunately you've been getting parts changers and guessers. I hope this is the same company and your not paying for repeat trips?

Ask for a senior tech, explain that you want this issue resolved!

HVACNUT

All easily diagnosed with the right knowledge and equipment.
Resistance and amp draw across the coils. Together and independently.
Static pressure across the air handler.
Humidity levels.
Blower motor RPM, CFM and amp checks.
Correct voltage and grounds, grounds, grounds.
Temperature rise across the coils.
Air filter.

Nobody snuck in in the middle of the night and changed the ductwork..

Jolly Bodger

Bad/corroded feeders? new thermostat finishing on high heat with no cool down time?

Agree, it's not a hard job for a good troubleshooting tech. Ductwork may still be inadequate but is not the cause of your issues. Something has changed.