is something wrong with my furnace?

[dtt454]

just a little background. older house built in 1954, looks like the date on this furnace tag is 1990. its a carrier model wavg55-ec ive owned the place for over 10 years and its always been this way as long as ive owned the place.

so, what it does, is when the thermostat is set to heat the exhaust booster fan comes on, and the thing lights like id expect. but it only burns for maybe 15-30 seconds, after the burners shut off then the main blower kicks on and runs for id guess maybe a minute. after the main blower stops the cycle starts over again. it works to keep the place warm but just seems to me that a furnace should not cycle on and off so much.

most every furnace ive been around, when the furnace kicks on it runs non stop till the place is up to temperature.

im wondering if maybe the thermostat might be wired wrong or maybe thats just how that furnace operates?

a few other details that might be useful. the house is not really that drafty, it has good insulation and it doesnt loose the temperature so fast that the furnace cant keep up. the thermostat is an older mercury one. ive had to replace the ignitor a few times over the years, and once i ended up putting a new control board in it (for the ignitor circuit being bad) i just took the part number off the old board and installed it exactly the same way as the one that came out. the furnace operation didnt change after the new board. (other than the ignitor started working)

just curious if maybe thats just the way this furnace works

 

[dtt454]

oh and i know photos always make things better.

 

[MFolks]

How clean are the air filters? Usually the blower needs to come out for a good cleaning if the filters are dirty.

 

[philjafo]

There is definitely something wrong with your furnace, it sounds like it might be shutting off on limit as in its not getting enough air flow and its overheating. In the serial number digits 3 and 4 are the year of manufacture, so it was made in 1993. Carriers also have a common problem of the secondary heat exchanger getting plugged up and causing it to overheat. I highly recommend you have someone that knows what they're doing take a look at it and run a combustion analysis on it.

 

[matouse3]

I had a similar problem, not exactly the same, but it turned out to be the batteries in the thermostat. Worth a look if you have a battery powered one.

 

[Falcon67]

Sounds like maybe a limit switch going bad. Had that on the unit at the old house. If the low limit is set too low, it'll shut off the burners just about time it triggers the blower. Blower cools limit switch, T-stat still calls for heat so when limit switch cools, blower shuts down, burners light and here we go again.

I replaced the limit switch, but the unit was so old that the generic replacement switches (tried several) were more sensitive. So in cold weather in a pier-and-beam house, the blower would kick on and start picking up cold air from the floor, which would cool the limit switch, which shut off the blower but kept the burners running. So the blower would cycle half a dozen times for a heat cycle. That's a cold leaky house LOL.

 

[pop pop]

At that age, you really need someone to take time to clean and thoroughly check out the system. I had an 88 model Carrier gas, and replaced it 7 years ago because the heat exchanger was rusted out.

 

[brewchief]

Definitely not normal operation, if it hasn't had a full and proper check up and cleaning in at least ten years it's time now.

Don't be shocked if it has a bad heat exchanger.

Try jumping the R and W low voltage wires at the control board to take the t-stat out of the loop, if it works properly then adjust the heat anticipater on the t-stat or replace with a modern electronic one.

 

[Rob_b]

I would suggest that the thermocouple may be the culprit. Its designed that if it doesn't see heat in a few seconds, it thinks the flame is not on and shuts the gas down to prevent a major gas explosion. Have some qualified inspect it. This is not time for a do it yourself

 

[dtt454]

just thought id post a followup in case you want to know what i came up with, one thing i should have said is the led on the board was not blinking any codes when it shut down. and i put a new filter in before i posted. anyways with chiefs advice i shorted the two terminals together and the thing ran till i was tired of holding the wire. which was about 10 minutes.

also just feeling the ducts by hand, which i know is not to accurate, they felt good and warm but not so hot you cant hold a hand on it or anything. ive been watching some youtube videos on setting the anticipator on the thermostat and i sure cant find the adjustment on mine.

i suppose ill just replace it with an electronic one.

thanks for the responses though.