2010 Warm Air When Engine Runs/On (AC Heater Servo Regulator 063800-1100)

The blend door does fail but it is not a common problem. Hot coolant is always flowing into the heater core (Heater Radiator Subassembly). If the air mix blend door is stuck open (D), heat will overwhelm ac cooling. If it is stuck closed (C) you get no heat.


In most cases when the engine stops, the engine water pump also stops. This would allow a stuck open heater core to cool off quickly when the AC was running.

This post gets into it a little more.
No Heat: Coolant Pumps During Main Mode, Not While Running | PriusChat

Accessing the blend door requires removing the dash. For AC cooling concerns, I might disconnect the heater hoses at the firewall and connect them together, bypassing the heater core as a test or summer long solution.

 

Yeah, the "blend" or "air mix" door actuator is on the not-easily-accessible side of the HVAC box in gen 3, very difficult to get to without extensive dash disassembly. (That's in contrast with gen 1 and gen 2, where that actuator was over on the driver's side of the box and easier to reach.)

So the official procedure in the repair manual starts with removing the dash. I might have seen one or two posts where some clever and determined individual found an alternative.

Issues with the air mix door and servo actuator can be mechanical or electronic. The door is moved by a servo motor and gear. The small wire harness that drapes over the HVAC box and connects to the motor contains a chip (right in the plug that plugs into the motor) that's responsible for tracking the position. So a problem with the chip can call for replacing that wire harness, a problem with the servo motor or its attached gearing can call for replacing that, or a problem with the door itself, the linkage that's part of the HVAC box, can call for taking that whole box out.

Again, clever determined people sometimes find alternatives. I did see a thread where somebody figured out the door itself had popped out of its linkage inside the box, which ordinarily would be the worst case for repair, but they managed to poke chopsticks or something up through the air outlets, maybe using a skinny inspection camera, and pop it back into place.

 

My exact situation… is I replaced the whole AC system last summer.

Including the evaporator inside the dash.

I tried to fix what wasn’t broken…

When I put the servo motors back, I must’ve not aligned the gears properly.

Everything was working, but when I’d change temperature from 72~ to 74~, I’d hear a clunk in the dash.

It kept clunking, but working, until it didn’t and it’s been stuck on max heat since.

(But when the engine turns off the heat goes away quickly)

I pulled the dash again in January… figured out the gear rail track the blend door uses is causing the clucking because it’s probably skipping a tooth…

I failed trying to fix it then.

I think the only info that could help me, is if anyone knows the default state the gears / climate control is in.

So I can reset / align everything.

Because when I manually move the black gear the temp mix servo motor attaches to, it also shifts air from the upper and lower vents, so I assume it works in tandem with air outlet servo motor.

Thank you to everyone in the PriusChat community, with a special shout-out to ChapmanF, your posts over the years have helped me tremendously!

Prepare for the revival of the classic “What did you do to ur Gen iii Prius today????”

 

There are three servos: inlet select, outlet select, and air mix.

I'd be surprised to see the air mix servo having any effect on the outlet select. Double-check you're moving what you think you are?

 

The problem has been solved!

The blend door is actually a plastic flap, somehow it folded over itself, (maybe when I replaced the evaporator…) allowing a gap for heat to pass.

 

That looks easy enough, not!

 

I’m just glad I didn’t have to drain the coolant or evacuate the AC Freon…

It took days to fix my tangled mess of aftermarket wiring… pictures coming soon!

 

I thought I'd never find that thread again, but it was Pyro da Cat, and long screwdrivers, not chopsticks. That was in a Prius c.

 

Ok I spoke too soon…

Still maximum heat…

Also still barely any airflow through the top…

Foot has good airflow.

My AC has refrigerant… but no cool air comes through…

All the servo motor gears spin nicely…

When I change the temperature, the motor for the air location also spins…

I’m surprised the plastic flap didn’t fix this.

It was folded over itself, in such a way which made the gear that move the blend door difficult.

Once I unfolded the flap, the gear spun very smooth.

Also, the air gets hotter when I set it to Low… it’s scorching hot… but when I put it on High it’s still very hot… but less so..

I’m so desperate now… I just spent $200 on that whole giant white plastic air box…87050-47150

It’s not going to arrive for a few days… I’ll take another look and then just replace absolutely everything….

Wow I hope I find the answer before I have to recharge the AC again…

 

I have a fun fact…

We all know the HVAC controls for the 2010-11 is different than the 2012-2015…

but actually the 2012 is different too…

I really wonder why…

I’ll report back if it works !

 

Alright… the blend door, which is actually two flimsy clear plastic flaps, hooked into a gear track, is fixed!

Here’s how they’re supposed to look. I had to buy a whole assembly just to see this, since nobody had any photos. Hopefully this saves someone $200 10 years from now.

Now cool outside air can enter the cabin once again!

But now I discovered another unrelated issue… my AC has a leak… still…

The fun continues!

Oh and the 2013 HVAC controls don’t work in my 2012. Some of the buttons don’t function. Fortunately my original controls are fine.