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I saw there was another thread but unable to respond to it. My A.C. cuts out after the car has been running a while but the fan still works and very little air comes out even on the highest setting. I turned it off and rolled the windows down for a bit. Then it worked great for about 5 minutes and went back to the same thing. I'd like to have an idea of what is wrong before I take it into service.
Thanks.
 

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Evaporator temp sensor is bad, the evaporator under the dash is turning into a block of ice. It should cut the compressor out at around 35F-40F.


There are a couple threads here about that. Easy to change usually and not expensive.
 

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I saw there was another thread but unable to respond to it. My A.C. cuts out after the car has been running a while but the fan still works and very little air comes out even on the highest setting. I turned it off and rolled the windows down for a bit. Then it worked great for about 5 minutes and went back to the same thing. I'd like to have an idea of what is wrong before I take it into service.
Thanks.
It may well be a sensor, but for a properly operating AC, the coils should not frost up if there is air flow. The reason is when refrigerant (aka freon) pressure is correct, the vaporization temperature should not be below 0C/32F. Ice cannot form above 0C.
First, do the simple thing - check if refrigerant charge is low. Because if it is low, it is cheap to fix. You can waste a lot of money changing other things. A low charge will result in low evaporator pressure - which will cause vaporization temperature to go below 0C. Frosting of coil happens and gradually blocks air flow. This does NOT mean you have a very cold discharge. Just localized frosting. Not intuitive I know.

Tell us where you live, climate (humidity & air temperatures has impact).
 

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Yes, the charge could be low, but be aware that variable displacement AC with auto blower speed most certainly can freeze up the evaporator (if the sensor isn't working) in the right conditions even with the correct refrigerant charge level.
 

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It is much cheaper to check the charge 1st, right?
If it is low, you need to fill it no matter what, if you want the AC to work properly.
 

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It is much cheaper to check the charge 1st, right?
If it is low, you need to fill it no matter what, if you want the AC to work properly.

Sure, it's easy to check if you have the correct tools and knowledge. To really be 100% certain of the charge level, you have to evacuate it and weigh the refrigerant back in. That's not cheap.



In any event, even if the charge is low, he will still have to correct the problem with the evaporator temperature sensor. If it were working correctly, it wouldn't let the evaporator freeze over, even if the charge is low. With a correct charge and bad evap sensor, he will still have problems with freeze over.
 

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So if he is not sure, change the sensor first? My point is, if you go to a shop and say it is the sensor or expansion valve most would just stick it to you. Fixing a low charge is low profit. I usually assume poster is not highly skilled in the craft... So, mechanics turning wrenches will cost $$. DIYer can change a sensor, even compressor for parts cost. Make the shop show it is not something simple.
 

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The sensor is testable. I do not suggest throwing parts at problems.



Is it your suggestion to ignore that the sensor (or whatever reads it) is clearly not working correctly? To each their own.
 

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I said in my 1st post, it could very well be the sensor. But check low charge 1st. I trued to offer a tech reason why it could be that simple. I teach this field, so i dont want to bang on it...I did not say red is wrong, I offered a different possibility, low charge - a very common problem with leaks, age, wear. Have you ever noticed aAC with a leak is always iced up?
 

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I said in my 1st post, it could very well be the sensor. But check low charge 1st. I trued to offer a tech reason why it could be that simple. I teach this field, so i dont want to bang on it...I did not say red is wrong, I offered a different possibility, low charge - a very common problem with leaks, age, wear. Have you ever noticed aAC with a leak is always iced up?

Okay, I see our difference here.
You believe that the problem is either low charge or bad sensor.


If you knew the system better, you'd know that it has to be a bad sensor, and it could also be low charge. I don't see anyway that it could be low charge only. The sensor would have shut off the compressor before the evap froze over completely.


I guess we'll have to wait to see what the OP discovers.
 

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More or less, no offense taken. Related topic, hvac pro's, (no diy advice there):
Low charge causing frozen evap coil?

I know about AC systems. I work on them. I know that low charge can cause evaporators to freeze over, and I know why. I don't dispute that at all, never have. (I do dispute that that is the only reason they can freeze over.)



Why do you dispute that the evap temperature sensor, when working, will turn the compressor off before the evaporator freezes over?
 

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You are now putting words in my mouth.
I said, "It may well be a sensor, but for a properly operating AC, the coils should not frost up if there is air flow. ....
First, do the simple thing - check if refrigerant charge is low. Because if it is low, it is cheap to fix. "
I now know why hvac pro's don't give diy'ers advice. Good rule. I'm moving on.
 

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I added a can today to my Accent. Last year I rebuilt the whole thing and fill by weight, But it never ran like the one in my Gen Coupe where it cycles with the evap sensor around 36F-38F after it's all cooled down, in recirc and low fan speed. Now it does , pressure is 45lbs and 275lbs at 90F.
 

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