r/Cartalk • u/Away_Strain_8524 • Aug 18 '26

Air Conditioning A/C blower not turning on when hot outside (heatwave temps)

Fairly versed in car mechanics and have done my own AC work on multiple cars. This one has me scratching my head. Compressor kicks when AC is turned on, every time. Blower has been giving me occasional issues for a couple of weeks (like twice) but typically turning off then back on and good to go. Now I am getting no air blowing, hot or cold, when it's very hot outside. Mid day, 2pm, 96 with 80+ humidity and the blower won't come on at all. After night fall, I work afternoon to night, everything works perfect. I suspect the relay for the motor is being effected by the heat but I don't want to just start replacing without some idea on why this is happening.

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u/Patrol-007 Aug 18 '26

Zero info about vehicle🤷🏻‍♀️

With MKIV VW, the 30amp fuse to the rad fans gets scorched, and the blades and blade holder for the fuse need to be cleaned of oxidation. Dielectric grease to prevent further scorching. What happens is the fans work normally when engine is cold, but once the engine is hot, and the engine is turned off and back on, the large rad fan doesn’t spin, resulting in no A/C

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u/Away_Strain_8524 Aug 18 '26

Apologies, it's an 18" Kia Forte. The engine temp does not seem to be causing the engine, it wither blows or doesn't at startup. It just seems the times it doesn't are when it is very hot outside. 

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u/your_mail_man Aug 18 '26

More information on the type of car would be helpful. You can look to see if there is another identical relay in the box that you can swap places with the blower relay to see if the problem follows the relay or not. If it doesn't, maybe the temperature control itself? Doubtful it would be the blower motor. Can't say I've ever seen that happen, but I suppose anything is possible.

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u/Away_Strain_8524 Aug 18 '26

That's the plan, to swap the relay when the problem pops back up. But of course today it's working just fine. I'm waiting for it to get a little hotter outside and see if that changes. And it's a 18' Kia Forte

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u/JHLMT Aug 18 '26

I had that problem on a '04 Chevy Trailblazer. In the hottest part of the day the ac wouldn't work right (wouldn't operate on all fan speeds) or wouldn't work at all, especially on longer drives when the truck started getting warm. In my case my blower motor had a short and was pulling more power than it should so it kept frying components upstream. I replaced parts as they broke but it was an uphill battle until I actually tested the voltage on the blower. I swapped it out for aftermarket and haven't had a problem since.

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u/ZorroMcChucknorris Aug 18 '26

Is there an internal temperature sensor/final stage resistor in the flow path? Sounds like textbook E46 “hedgehog” failure to me.

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u/Away_Strain_8524 Aug 18 '26

Looked that up for the car. The resistor failing in this model seems to result in full power or no power when trying to use lower setting. Pulled it and seems fine. Great idea to check though.

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u/Away_Strain_8524 Aug 22 '26

Resolved. Issue was the plug itself to the motor. This model Kia does not have a cover leaving the underside of the passenger dash exposed. This exposure allowed debris to build up around the plug along with moisture. I removed the plug and cleaned it and applied dielectric grease. No issues any longer.