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Why is my fan running all the time with no heat

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Language: en

00:00:04.250
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00:00:06.990 00:00:07.000 okay what's going on
00:00:09.310 00:00:09.320 I got a furnace sitting down here and
00:00:13.390 00:00:13.400 the fan comes on but the heat don't come
00:00:16.420 00:00:16.430 on all does blow cold air so I come down
00:00:21.400 00:00:21.410 here and I'm looking at this furnace and
00:00:23.620 00:00:23.630 this one's about 20 years old so where
00:00:28.179 00:00:28.189 do I go next why is this thing doing
00:00:30.310 00:00:30.320 this okay you take a look at the
00:00:32.380 00:00:32.390 thermostat the thermostat when you look
00:00:34.840 00:00:34.850 at the fan it's in the auto position so
00:00:38.020 00:00:38.030 it shouldn't be running all the time it
00:00:39.850 00:00:39.860 should only run when the furnace is on
00:00:42.240 00:00:42.250 so what's going on well here I'm showing
00:00:47.470 00:00:47.480 a bunch of limit switches this is an old
00:00:50.440 00:00:50.450 old style that's gonna find this furnace
00:00:52.810 00:00:52.820 built a little well over 30 years ago
00:00:55.710 00:00:55.720 combination fan and limit there's a
00:00:58.000 00:00:58.010 little button type limit switch here's
00:01:01.930 00:01:01.940 another one that's got a probe this one
00:01:03.940 00:01:03.950 here of course has a probe it fits
00:01:06.310 00:01:06.320 inside the ductwork these two are also
00:01:09.429 00:01:09.439 these are newer styles that are used in
00:01:12.789 00:01:12.799 somewhat newer furnaces and the switch
00:01:16.599 00:01:16.609 is right there and it's put in the air
00:01:22.690 00:01:22.700 flow to sense the temperature the air
00:01:26.260 00:01:26.270 passing across it if the air reaches too
00:01:30.099 00:01:30.109 high a temperature it does what we call
00:01:33.340 00:01:33.350 limit out well how these things work is
00:01:37.270 00:01:37.280 one that temperature is too high it
00:01:42.309 00:01:42.319 shuts off and it shuts off the gas
00:01:44.349 00:01:44.359 supply or with an oil furnace and oil
00:01:47.230 00:01:47.240 supply so it shuts down the heat source
00:01:50.520 00:01:50.530 now if it cools back down most of these
00:01:54.550 00:01:54.560 will turn back on there are some that
00:01:57.069 00:01:57.079 you actually have to push a button on
00:01:58.749 00:01:58.759 because they're called manual reset but
00:02:01.389 00:02:01.399 these are all automatic reset so if the
00:02:03.879 00:02:03.889 temperature goes down they'll come back
00:02:07.480 00:02:07.490 off usually sometimes they go kick off
00:02:12.490 00:02:12.500 so many times that they'll actually fail
00:02:14.500 00:02:14.510 okay
00:02:16.190 00:02:16.200 why did they kick off because you didn't
00:02:19.040 00:02:19.050 have enough airflow most common reasons
00:02:22.520 00:02:22.530 for not enough airflow is a plug filter
00:02:25.660 00:02:25.670 plug filters usually are what get these
00:02:29.630 00:02:29.640 things going add when you take and put a
00:02:33.949 00:02:33.959 new filter in if the limit has not worn
00:02:37.460 00:02:37.470 out and failed completely then it'll
00:02:40.790 00:02:40.800 start working normally but sometimes
00:02:44.750 00:02:44.760 that doesn't happen and what the
00:02:46.699 00:02:46.709 symptoms of this are is when the furnace
00:02:49.400 00:02:49.410 comes on it usually runs about four or
00:02:52.850 00:02:52.860 five minutes sometimes it'll run longer
00:02:56.930 00:02:56.940 and then it shuts off a fan continues to
00:03:00.890 00:03:00.900 run but the burner shuts off so with the
00:03:03.770 00:03:03.780 burner off of course it cools down and
00:03:06.589 00:03:06.599 that fans gonna stay on now on most of
00:03:09.920 00:03:09.930 the newer furnaces now if the course if
00:03:13.100 00:03:13.110 it cools down enough goes below its
00:03:15.680 00:03:15.690 reset temperature then it comes back on
00:03:18.620 00:03:18.630 it starts working normally so you may
00:03:20.690 00:03:20.700 not even notice what's going on for
00:03:23.930 00:03:23.940 quite a while until it gets really cold
00:03:25.699 00:03:25.709 and because it's not running all the
00:03:29.150 00:03:29.160 time it doesn't maintain the temperature
00:03:31.990 00:03:32.000 so let's say I've gone out there and I
00:03:36.250 00:03:36.260 replace my filter and it still does it
00:03:39.729 00:03:39.739 so what else could do it well here's
00:03:42.710 00:03:42.720 another reason why you may not get
00:03:45.229 00:03:45.239 enough airflow through that furnace this
00:03:47.930 00:03:47.940 blower now this is a nice clean blower
00:03:51.620 00:03:51.630 here but if this thing is filled with
00:03:55.670 00:03:55.680 dirt and make a cat or dog hair all over
00:03:58.729 00:03:58.739 here and these little slots they're all
00:04:03.830 00:04:03.840 filled up full of dirt it's not going to
00:04:06.410 00:04:06.420 move very much air so you may actually
00:04:08.390 00:04:08.400 have to clean that thing so is there
00:04:11.990 00:04:12.000 anything else that could cause a limit
00:04:15.080 00:04:15.090 to kick off well there's a few odd
00:04:17.839 00:04:17.849 things if the furnace is over fired when
00:04:21.710 00:04:21.720 it was new it can do it there's some
00:04:25.010 00:04:25.020 ductwork problems that's kind of beyond
00:04:28.010 00:04:28.020 the scope of this video but
00:04:29.749 00:04:29.759 I would be looking first plug filter
00:04:33.999 00:04:34.009 plug blower something like that now I I
00:04:39.019 00:04:39.029 have videos on you know going farther on
00:04:42.409 00:04:42.419 some of this stuff and I will have links
00:04:46.610 00:04:46.620 here at the end of this thing to a
00:04:48.950 00:04:48.960 couple more videos but mostly what
00:04:53.239 00:04:53.249 you're going to encounter is plug
00:04:55.790 00:04:55.800 filters or plug blower wheels the simple
00:04:59.029 00:04:59.039 repair actually cleaning the blower is
00:05:01.879 00:05:01.889 not quite that simple but certainly
00:05:03.769 00:05:03.779 changing the filter is that's it on the
00:05:06.439 00:05:06.449 first things you do if your limits which
00:05:09.200 00:05:09.210 kicks off that's it on this one

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