From cold air to instantly hot air? Any Ideas? - Smart Car Forums
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post #1 of 11 (permalink) Old 08-02-2010, 06:43 AM Thread Starter
 
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From cold air to instantly hot air? Any Ideas?

So I did read the threads about the unit freezing up, I think this problem is different than that one.

I was driving along, after having cold air for most of my ride it instantly turned to hot air in about 5 seconds. It wouldn't go back to cool air, I tried turning it off for a minute but nothing. I have never had an issue with the AC, it has always worked really well and was very cold.

  • 70 degrees outside
  • low humidity
  • using external air (no recirculation)
  • air was set on low fan speed
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post #2 of 11 (permalink) Old 08-02-2010, 06:56 AM
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Given your description, it sounds like the logic that controls the A/C was corrupted. Logic can be changed when a relatively benign part goes open or shorts. For example, a piece of debris across two pins causing a short on a temp gauge or temp sensor, as opposed to, say, freon leaking out.

But, it could be any number of things and we could speculate all day long. I think this means a trip to the dealer for you....

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post #3 of 11 (permalink) Old 08-02-2010, 06:57 AM
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Key phrase is " air was set on low fan speed" when there is not enough air circulating through the unit, it can freeze up. It does happen on just about any AC unit. There are sensors that are supposed to keep it from happening but only if they ice up where the sensor is. It can take a lot longer than a minute to thaw them out. try turning on the warm air and let it run for awhile.

What can happen is at lower speeds, water vvapor removed from the incomming air wil stay suspended on the cooling coil and then freeze because the air can't go through the water. You may notice on some AC units, when you turn them off, water wil come pouring out. That is normal. Just the water running off the cooling coils.
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post #4 of 11 (permalink) Old 08-14-2014, 10:08 AM
 
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I'm having this problem for the past day.

Again, I think similar to the OP, the A/C was NOT engaged. It was just on FAN, no recirculate, outside temp was 65 and felt great, but then it would switch to HEAT and blow hot, easily 80+ degrees, and then back to cool. No audible switch was heard, nothing happening with the AC going on or off, but just hot air. At first I thought I went through some form of hot air patch in the external environment, but since it kept happening over and over again on a 50 mile journey at mostly highway speeds, I figured it was in the vehicle.

Any thoughts?
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post #5 of 11 (permalink) Old 08-14-2014, 10:33 AM
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Your problem may not be AC related specifically, but you might check this thread about a sensor that can be broken in the passenger footwell. Also, there is a suggestion in this thread about cycling the temperature lever back and forth. Couple shots in the dark anyway:

https://www.smartcarofamerica.com/for...-sensor-43946/
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post #6 of 11 (permalink) Old 08-14-2014, 01:36 PM
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Quote:
Originally Posted by ryan112ryan View Post
So I did read the threads about the unit freezing up, I think this problem is different than that one.

I was driving along, after having cold air for most of my ride it instantly turned to hot air in about 5 seconds. It wouldn't go back to cool air, I tried turning it off for a minute but nothing. I have never had an issue with the AC, it has always worked really well and was very cold.

  • 70 degrees outside
  • low humidity
  • using external air (no recirculation)
  • air was set on low fan speed
The next time it does that move the temperature lever up and down full scale several times and see if that corrects the condition.
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post #7 of 11 (permalink) Old 08-14-2014, 06:54 PM
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if AC was not on and your temp set up to say 70, the sensor could be calling for heat if the outside air was 65. just a thought
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post #8 of 11 (permalink) Old 08-15-2014, 05:24 AM
 
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Sounds like a stuck air door or heater control valve. Even with the new fancy controls most all climate systems have a valve that allows hot coolant to flow when you want heat and not flow when you don't. Also there are little air flow doors in the unit that move to allow Ac/heat, feet, mid level, defrost and combinations. I would suspect either the control unit has hiccuped or a servo has died. These kind of things make me dream of my older stuff where these are controlled by push pull cables. Easy to diagnose that stuff.
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post #9 of 11 (permalink) Old 08-15-2014, 03:19 PM
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Quote:
Originally Posted by squatch View Post
Sounds like a stuck air door or heater control valve. Even with the new fancy controls most all climate systems have a valve that allows hot coolant to flow when you want heat and not flow when you don't. Also there are little air flow doors in the unit that move to allow Ac/heat, feet, mid level, defrost and combinations. I would suspect either the control unit has hiccuped or a servo has died. These kind of things make me dream of my older stuff where these are controlled by push pull cables. Easy to diagnose that stuff.
The smart has no heater valve. Coolant flows through the heater core at all times. The blend air door controls the temperature output. If it was stuck the temperature would not change at all.
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post #10 of 11 (permalink) Old 08-15-2014, 07:33 PM
 
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I stand corrected. Just shared general knowledge based on past experience. Haven't had a need to tear apart the smart heater so far. There are quite a few things on these cars that are different than most.
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