dslreports logo
site
 
    All Forums Hot Topics Gallery
spc

spacer




how-to block ads


Search Topic:
uniqs
15619
share rss forum feed


aaronfitz
Premium
join:2004-03-06
Cedar Rapids, IA

Furnace Blows Cool Air About 1/2 the Time

Click for full size
Click for full size
Click for full size
Click for full size
Hello,

Currently, I have a rental unit through a property management company that is known for its not-so-great maintenance around here. I moved into this apartment knowing this because I thought the tales were a little exaggerated, and the building I'm in was built a mere 4 years ago. The building also seems to be built very solidly, so I'm not expecting any other issues. I'm ready to try and resolve this myself, so I'd appreciate more than just "keep calling the landlord" replies...

About two months ago when it started getting cool around here, I noticed that at times my furnace would blow out cool air at times. I went into my utility closet and discovered that when this is happening, the furnance is not lit, but the fan is on. This typically happens when the temperature shown on the thermostat is showing 1-4 degrees below the programmed desired temperature. However, sometimes I can toggle the thermostat from heat/off/heat a few times and the funance will kick on. Sometimes the heat just refuses to come on. There are times that when the system starts blowing out cool air, my apartment will actually warm up a little on its own (I'm in the middle of three floors) if I turn the thermostat off.

When I first contacted the property management company, they sent someone out who claims he changed my thermostat when I was at work. In the last month and a half, I have gotten nothing but promises from the property management company. Apparently intermittent heat is good enough for their standards.

Even with the (hopefully) new thermostat, the system is still not functioning correctly. I have an inkling that the heat anticipation is not working correctly. Is this a function of the thermostat? Is there any way to tune it/disable it? Is there anything else I can check?

I should note that when the furnace is actually lit, it heats the apartment very well.

Pictures attached, let me know if any clarifications would be useful. I'm also not sure if these pictures will be particularly useful..


Warzau
Premium
join:2000-10-26
Naperville, IL
kudos:1
So the blower comes on on it's own. Or is it after the heat cycle?


yock
TFTC
Premium
join:2000-11-21
Miamisburg, OH
kudos:3
reply to aaronfitz
This sounds like normal operation. Most furnaces will continue to run the blower after dousing the burner to utilize the residual heat remaining in the chamber. The characteristic of such operation would be that it shuts off just a couple degrees from thermostat temperature. The system will also start with cold air since the air in the ducts hasn't been heated by the furnace.

I'm no expert, but what you're describing sounds perfectly normal. If anything, the furnace's internal thermostat, the one that measures the air temperature at the burner, might be malfunctioning.


Phil
Rojo Sol
Premium
join:2001-06-11
Downers Grove, IL
kudos:2
reply to aaronfitz
The heat shuts off on my furnace about two minutes before shutting off. This is done to cool the heat exchangers.


CatSnak
RIP Splashy - We miss you
Premium
join:2001-05-06
Lakeside, CA

2 edits
reply to aaronfitz
said by aaronfitz:

I have an inkling that the heat anticipation is not working correctly. Is this a function of the thermostat?
No, it's a function of the furnace itself. There is a thermal switch mounted in the heat exchanger that closes the contacts to the fan circuit when the heat exchanger reaches a desired temp it also keeps the fan running after the burners have gone out to cool the heat exchanger nad then opens the circuit once a desired temp is reached.

I would suggest monitoring the furnace for the proper operation of the switch. Set your T-stat a couple of degrees above room temp and see if it acts as I mentioned. Beyound that you'll more then likely need a licesned repair tech to come and diagnose the problem.
--
Founding member, 2002-2003, 2005-2006 Director of Communications, 2004-2005 Secretary for the Crunchenstein Project


Warzau
Premium
join:2000-10-26
Naperville, IL
kudos:1
reply to aaronfitz
Yup agreed with everyone so far. If it's after a heat cycle, it's normal. from 30-1 min.


eXodus
Premium
join:2005-08-04
Rockaway, NJ
said by Warzau:

Yup agreed with everyone so far. If it's after a heat cycle, it's normal. from 30-1 min.
Agreed mine does the same.
--
-eXodus


SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3
reply to aaronfitz
From what I can gather from your post, the blower operation you are experiencing "1/2 the time" is not a normal function of the furnace operation. You stated in your post that this happens "when the temperature shown on the thermostat is showing 1-4 degrees below the programmed desired temperature." That statement tells me the furnace and/or the blower should not be operating at all. Yet, you say the blower is running. Plus you say the air coming from the ducts is "cool air at times." Something is up.

The next time this happens, do not mess with the thermostat, do not open the blower compartment and/or do not kill the power to the furnace. Look through the site glass in the blower compartment door. Look for an led light. Watch the light and make note of the flashes. Right below the site glass is a legend showing the LED status codes. Say, for instance, there is a malfunction of the furnace, such as a flame roll-out condition. The LED light would blink once, a pause, then it would blink three times, indicating status code "13". See if you're getting any status codes.

FYI, if there is a power interruption when the furnace is calling for heat, the blower will come on and run for 90 seconds after power is restored. Then, the furnace will go into its normal heating cycle.


jrs8084
Premium
join:2002-03-02
Statesville, NC
kudos:1
Reviews:
·AT&T U-Verse

1 recommendation

reply to aaronfitz
From the date code on the thermostat, I would say it is a new one. But, even though the 'stat may have been changed, were fresh batteries installed? Bad batteries can cause some odd issues. I would try replacing them with fresh ones first.

Yes, a furnace such as yours does have a cool down cycle (in you case, this is handled electronically-as evidenced by the LED code service tag on the front of the unit). But, from your description, the burners won't come on even when the 'stat hasn't been satisfied.

The heat anticipation and "swing" is a function of the thermostat, but even if you have a larger "swing", the furnace should do nothing until the lower threshold has been reached. It shouldn't turn on just the blower.

I would put in new batteries in the unit, and, with the help of a partner, set the furnace for a call for heat. Depending on the thermostat, you might have to wait a bit before it begins preheating. Watch to see if the blower turns on, or if the burners do light, but shut down prematurely. Note any LED flash codes. Post back.
--
512Ke, LC, Classic, Qudra 605, Centris 610 AV,Performa 6112, PM 6500, Cube, iMac G4 17", iMac 24", PB 5300, PB 3400, PB G4, and a few PCs


aaronfitz
Premium
join:2004-03-06
Cedar Rapids, IA

1 edit

1 recommendation

reply to aaronfitz
I should've made something a little clearer -

By 1/2 of the time, I mean that about 1/2 of the time that the furnace should kick on and generate heat, it doesn't. It may not be 1/2, but I meant that sometimes it heats, and sometimes it doesn't. When this happens, the fan kicks on but the furnace never lights. If left unattended, the fan will blow for hours and the furnace will never light. I am aware that the fan blowing for a minute or so after a true heating cycle is normal.

It just so happens that the maintenance company finally came out again today. The card doesn't say what exactly they tried this time, but hopefully they caught the issue. I still say two months is a horrible turn-around for an intermittent issue. I could understand it taking a while to resolve, but there was over a month and a half lag between visits

I'll take a look at the mentioned LED if this happens again and check in. I didn't realize it would flash status codes, I just thought it was a power indicator. I'll also change the batteries on the thermostat..


SandShark
Long may you run
Premium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3
That's a little more clear. Thanks.

Now, you're saying the blower is running continuously (for hours), but the furnace never fires. From my recollection of servicing this particular model furnace, if there is a call for heat and the furnace fails to fire, after several attempts (somewhere between 3-6 tries), the furnace will lock out and the blower will run continuously. There are a few things that could cause the furnace not to fire or fire and shut down (ignitor, flame sensor, flame roll-out, high limit, auxiliary limit). The LED status codes will tell you what caused the lock out.

Hopefully, it's fixed for good and you won't have to worry about it any longer.