Heating unit blows warm air then turns to cold air

If your system starts to blow cool air when your Nest thermostat is in Heat mode (or if it blows warm air when its in Cool mode), change the settings for orientation of your heat pump. The instructions depend on which thermostat you have

The cold that you describe may be just unconditioned air? If you are certain you can hear the comp operating for a couple of minutes, and then the heat starts, I would guess it is a reversing valve issue if it's a heat pump and it probably is. Or the control board acting up. I've had a lot of issues with the boards in the Amanda PTAC units. I can't remember how to configure it, but if you Google "Amanda ptac configuration", there is a lot of info online. May try a reset method first. Hope this helps!

heater blows cold air idle chrysler 300 Questions & Answers ...

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I just experienced this problem myself. What helped me was cleaning out the lint trap. My guess is that the until sucks in air through there, then conditions it. Blows the cold air out the top, and hot air out the tube. When it can't suck a decent amount of air in, the condenser can only condense so much of that limited amount of air. When it runs out, the unit just runs the fan until enough air has been condensed.

My lint trap was filthy, hadnt Bern cleaned in years. Soon as I popped it off, the unit started belching out cold air nonstop. Clean your lint traps! Don't make my mistake!

check to see if your cooling fans are working because when they dont work, your air will blow nice and cold when driving but will be hot air when stopped in traffic.

do you have an automatic change over thermostat? this would switch it from heating to cooling.

freon is low or outside is very cold

I have the similar problem with both my Jaguars, one is a 1988 Jaguar XJS, the other is a 1987 Jaguar XJ6, both blow COLD air out some vents while it blows warm air for heat. I heard it had something to do with the cold air blowing as a dehumidifier, I don't know if this is true, but it is really annoying to have both cold and warm air blowing when I need heat in these cold Canadian winters. If you find out please drop this website a note and let us know how you solved it. thanks.

First you have to identify what causes the problem.
To do this you have to:
1) When engine is cold check the level of coolant. If it is low fill it up.
2) Start engine and check if engine reaches regular temperature. If your engine is not heated enough it means your thermostat does not work properly and should be replaced.
3) If engine temperature is normal, then check the temperature of pipes that go to/from heater core. These pipes are located up the fire wall (easier access is from the passenger side). If pipe/pipes are cold (even engine is worm) it means you heater core is plugged and should be flushed. Keep in mind, flushing the whole cooling system is different from flushing heater core.
4) If pipe/pipes are hot/warm, turn off the fan, switch controller to the hot position, wait for 3-4 minutes and turn on the fan. Note if the cold air blows first or warm air blows first but it cools down in 5-10 seconds. If the air blows cold than it is most probably the problem with blend door or blend door actuator.
5) If air blows warm first and then cools down, then while running engine and remaining the transmission in PARKING position, press on the gas pedal until your engine reaches 3,000 RPM. Check if your heater blows warm/hot air. If it does, then your water pump does not work properly and should be replaced. If the air still cold, I would suggest to flush the heater core.

It sounds like you have a unit called a heat pump. When a heat pump unit is in cooling mode the outside unit blows hot air and the inside unit blows cold air. If the outside unit is blowing cold then the indoor unit is most likely blowing room temperature or warm air. It sounds like the thermostat could be controlling incorrectly or you could have a failed reversing valve which is the device that switches the unit from heating to cooling mode.