My fan speed stays low unless I change the temp to the extreme. So when it's 70 degrees out, and i set it to 61 degrees, the fan is slow. I have to drop to to 60 for it to blow harder.
Is there a temp sensor or something i need to replace to get it to vary the fan speed like it used to?

 

I changed one of these (#3 below) on my mother's car, years ago, when fan speed adjustability was lost to either high or low.
Search the part number on rockauto, the highest priced aftermarket units are half the price of OEM.

 

Thanks Zeta. I'll check out the transistor and see how it looks. 79330-S0K-A01 seems to be the correct part number, with lots of options available on ebay or rockauto.

 

So you can't manually control the fan by taking it off "Auto"?

Mine is a Navi so manual fan controls are on the screen. While in Auto mine behaves the same way. If it's 70 outside but my TL's been sitting outside, in the sun, windows closed, it can reach over 100 inside. Turn on the AC set to 65 and everything roars for a few minutes, then the blower slows down as it starts to cool off inside. However, it's not cool enough so I can either drop the temp setting lower or turn off Auto and use the manual fan controls to set back to maximum. Once I'm comfortable, I return the settings back.

 

I can manually control the fan speed, it's the Auto that doesn't work. So if it's on Auto at 65 and it's 100 degrees in the car, the fan speed will be low. I have to drop the temp to 60 for it to blow stronger. So it's not capable of ramping up/down on Auto anymore. I've been driving with it at 60 since 61 is too hot. The AC works fine, it's just the Auto & fan speed.
I wasn't sure where to start troubleshoot. I thought maybe it could be the in-car temperature sensor or even the sunlight sensor. Zeta pointed me to the power transistor which i can check first.

 

If you can still manually control the fan speed as indicated below, when taken out of 'automatic mode, the issue is probably not the 79330-S0K-A01 HVAC blower motor control unit.

 

If that's the case then maybe i'll try testing the in-car temperature sensor. page 21-53 (1485 of the pdf) has the steps to check resistance of the sensor. Not sure if replacements are readily available.

 

Have you tried running the climate control self-diagnosis function?
If there is a DTC present it could help point the direction to take.
The below is out of my CL FSM; however, it should be similar for your TL-S.

 

I ran the diagnostic and got code K for the air mix motor which seems a little weird since that part seems to be working fine.

 

Yeah, outside air temp, inside air temp, sunlight sensor all fusing together to support "The system automatically selects the proper mix of conditioned and/or heated air that will, as quickly as possible, raise or lower the interior temperature from its current level to the set temperature." (from my owners manual).

Have you taking any temp readings at the outlets for different temp settings on the dial? Setting to 60 basically turns all this auto stuff off and the AC runs at full cold.

Another thing that impacts mine, is my interior is all black. Once heat soaked, it does take a while for it to cool down. With the inside air temp sensor under the dash, I just don't think it reads the true temp inside the cabin. Just like the outside one is in the shade. They only read the temp in their exact spot.

Just like the thermostat in my house. It's mounted on the wall that encloses my heater. When the heat shuts off at my set temp, lot's of other spaces are as much a 4-5 degrees cooler. Therefore I compensate with the temp setting a bit higher.

 

Regarding the K code, if you swing the temp from 60deg to 90deg and back, do you feel the air temp change fairly quickly?