Heater blows cold unless you crank it to 90! Any thoughts?

[Brewcity]

Hey all....I noticed that my vents are blowing cold air, even if I have it set to say 75-80.
I need to crank it all the way up to 90 in order for it to start blowing hot.
Once I dial it down to say 75-80 again, it blows really cold air....as if the A/C is on (its not, I made sure).
Also...if I crank the vent to speed to high...it really doesn't seem likes its on high...it seems very weak.
Any thoughts as to what I need to check?
Thanks so much for the help! I REALLY appreciate it!

 

[M1Gunner]

What year is it and do you have manual or auto hvac?

 

[PG01]

M1 is right year/model/auto info helps
First thing i would check is to makes sure your filled up with antifreeze and we'll go from there

 

[sumo]

many things that can cause this. Blend door problem, Coolant level, Weak Blower motor, Clogged heater core

 

[about20ninj45]

Blend door actuator

 

[mportkiller]

Did the battery die? If so, there is a procedure to reset the digital temperature control. Something like turn the key to the on position, raise the temp all the way up, then all the way back down, then turn the key off and start it. It's something like that, but you can Google it too.

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[mportkiller]

Or this...

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[Matahoe]

Also...if I crank the vent to speed to high...it really doesn't seem likes its on high...it seems very weak.
Any thoughts as to what I need to check?

Along with checking the obvious under the hood like coolant I would start here and check to make sure your motor and resistor pack are working correctly. Sounds like you are missing 4 and 5 blower speeds which is likely the resistor pack. So check and make sure the fan is operational first because everything else in the HVAC system depends on this part.

 

[Brewcity]

Thanks to all...so sorry for the delay...was away for work.
I have a 2005 Yukon for those that asked, and its dual climate control.
I will look at these procedures this weekend, and report back.
Thanks again everyone! I truly appreciate it.

 

[HiHoeSilver]

Thanks to all...so sorry for the delay...was away for work.
I have a 2005 Yukon for those that asked, and its dual climate control.
I will look at these procedures this weekend, and report back.
Thanks again everyone! I truly appreciate it.

There is another reset you could try.

With the truck running, turn all temp controls all the way down, and then turn all hvac systems off(including the rears).

Remove positive battery cable for at least 10 minutes.

Touch the positive battery cable to the negative battery terminal (DO NOT bridge the two battery terminals).

Reinstall the positive battery cable.

Start the truck.

DO NOT touch anything for at least 15 minutes.

The hvac system will reset and run a calibration of all the blend door actuators and sensors, etc. on its own.

Costs nothing, takes 1/2 hour. Worth a try.