No Heat from a/c vents

[buzzmatrix]

So, This morning it's about 18°C outside and I start my car as usual, set the a/c to 28°C (max temp) and blower to auto at the lowest setting and drive to work. Usually the a/c start blowing air slightly above ambient 1-2 minutes into my drive but it was still blowing air at ambient temp halfway into my commute and it still was when I got to work! What the hell!

The engine oil was up to temp, so I'm assuming the coolant would be too and hence it's not an issue with the thermostat being stuck open. The air does get cold when I the a/c temp is set to the lowest at 16°C. I noticed that the air does get slightly warm when I switch off the a/c button at 28°C. So could it be the mixer valve after the a/c evaporator?

I also had the waterpump and thermostat changed recently within 500 miles. Is there a air bubble trapped in the heater core section of the coolant line? but I'd imagine it's a bit too many miles after a coolant change for air pockets to form and cause issues. Which leads me to think maybe it's the mixer valve. I don't smell any coolant through the a/c vents too, so it's most probably not the heater core leaking.

I haven't been able to plug in an OBD reader and pull any codes. I'm not even sure if this issue would generate any codes. I will try to pull any codes from the MHD app once I get my cracked screen fixed today.

Has anyone had this happen before? I did a quick search on the forums and google and I didn't find anything close to the issue I'm facing.