Heater blowing lukewarm air on lower settings

DJHUBBA

MEMBER
2001 DODGE RAM
5.9L
V8
4WD
AUTOMATIC
130,000 MILES

Flushed system, replaced heater core, new thermostat. Blows lukewarm air on the lower two settings and cold air on the higher two settings. The blend door is working as it should be. Any ideas? Any help would be greatly appreciated. Thank you.

Friday, April 24th, 2020 AT 2:28 PM

3 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Couple questions. When you say lower and higher setting, are you talking about the floor, dash and defrost vents or the fan speed?

https://www.2carpros.com/articles/car-heater-not-working

As for the blend door operation, how did you confirm it is operating as designed. I suspect we are missing something because it appears you covered the basics. Worst case, we are going to need to measure temperature of heater core lines and see what temp the hoses are compared to the other radiator hoses. You can use an infrared temp meter to do this. Let me know and we can go from there. Thanks

https://www.2carpros.com/articles/how-to-use-an-infrared-temperature-meter

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Friday, April 23rd, 2021 AT 11:00 AM

DJHUBBA

MEMBER
2 POSTS

Hello. Thank you for your response. Lower and higher settings is reference to the fan speed. If I am on any of the area settings I get this result. If I turn on the A/C then the lukewarm air gets hot. But only on the breast/face area setting. And still, if I put the fan up to high or just one notch under high. The air goes cold. (The A/C is void of Freon due to a leak) With the blend door, I took it off and verified nothing was broken and that the switch actually worked. I do have a laser thermometer but I have not checked it. I can tell you I have put my hand on the hoses and they are all super hot. So, I'm kinda lost. Not sure what to do.

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Friday, April 23rd, 2021 AT 11:00 AM

KASEKENNY

MECHANIC
18,907 POSTS

Okay. I am just trying to make sure we are on the same page. Your issue is that the air does not blow hot enough and you are not worried about the A/C because you are aware of the leak?

So if you heater hoses for the heater core are getting hot but yet you still don't have hot air when on heat? However, when the A/C is on, the air gets hot?

If this is the case, then I suspect you do have a blend door actuator issue. It may not be the actuator doesn't work but if it is not set correctly then when it moves it is allowing air over the heater core when it shouldn't. Take a look at the diagram. Air always passes over the evaporator but if it is not on then it is not cooling the air. The heater core always has hot coolant going through it so it is blocked off by the blend door when hot air is not needed. So if you are getting hot air on A/C and not on heat then the blend door is allowing the air to pass of the heater core when it shouldn't.

Does that make sense?

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