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Old 10-26-2021, 09:17 AM   #1
marinemama
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Furnace blowing cold air

The furnace is blowing cold air from the ducts, but the exhaust is hot.

2017 Keystone Springdale trailer.
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Old 10-26-2021, 03:49 PM   #2
JRTJH
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It does take 2 or 3 minutes for the furnace to clear the "static temperature air" out of the ductwork, but after that delay, there should be warm air at the registers.

Is there "cold air being blown out of the registers" or is there "no hot air being blown out of the registers" ???

If the exhaust is hot, that means the "heater box is hot" and the fan should be blowing hot air. If the ducting is not connected to the furnace air box, then there would be "no air blowing out of the ducts". If the ducting is connected to the furnace air box, then it should be hot air being blown out of the ducts...

I don't think I've ever seen a furnace system that "blows cold air" if the exhaust is hot. I have seen several that "blow hot air" but with the ducting not connected, it isn't getting to the registers... In all of those situations, there was "NO AIR" being blown out of the registers, not "cold air" being blown out of the registers....

So, is there "cold air blown out of the registers after a reasonable delay for the ambient air to be forced out of the ductwork" or "no air blown out of the registers" ???
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Old 10-26-2021, 06:39 PM   #3
flybouy
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Quote:
Originally Posted by marinemama View Post
The furnace is blowing cold air from the ducts, but the exhaust is hot.

2017 Keystone Springdale trailer.
Has it worked previously or is this a new to you camper?
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Old 10-28-2021, 06:20 AM   #4
marinemama
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Thanks for your reply. It blows hot air for five or ten minutes and the furnace shuts off. The thermostat was set for 80 degrees.
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Old 10-28-2021, 07:12 AM   #5
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Originally Posted by marinemama View Post
Thanks for your reply. It blows hot air for five or ten minutes and the furnace shuts off. The thermostat was set for 80 degrees.
Well did it get to 80 degrees? If so then normal operation, if not then maybe high limit temp sensor.
Gas furnace will blow cold/cool on startup until it fires and heat exchanger heats up, then fire shuts down and blower runs for about a couple minutes to cool down the heat exchanger.
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Old 10-28-2021, 07:22 AM   #6
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Could also be a faulty thermostat
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Old 10-28-2021, 07:24 AM   #7
JRTJH
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So the problem isn't that the furnace "only blows cold air" but rather "that the furnace works normally, but then shuts off and blows cold air. Depending on the thermostat setting, if the interior temperature reaches the thermostat setting, that is the "normal furnace sequence of operation"... If the interior temperature is not reaching the thermostat setting, you may have a problem. Here's a couple of possibilities:

If there is a heat duct "blowing hot air at the thermostat" or if the thermostat is in a location where the air is "hotter than where you're sitting" then the furnace will not "evenly distribute warm air throughout the trailer interior"... Truth be told, every trailer I've ever been in has "hot spots and cold spots" that seem to never cool down or never get warm no matter where you set the thermostat temperature.

Take a look at your trailer and determine if the thermostat, or the temperature sensors (hidden behind little plastic discs with holes in them) are situated where hot air from a duct can artificially alter what they sense. You may find that just putting a small plastic cover (try first with a 5 ounce paper cup taped over the sensor or a Tupperware container taped over the thermostat) will prolong your furnace run time.

If that doesn't resolve your issues, you may have a thermostat "high limit switch" that's locking out the furnace. That could be from a faulty high limit switch or from a blocked/insufficient duct air flow.
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