Heater actuator woes

2019 Prius AWD-E LE with 70k miles.

Wife complained of no heat. Turned out to be intermittent heat. Auto/Manual, selected temp (including HI), selected vents had no effect. Antifreeze is full.

Parked car without heat, shut off. 90 seconds later the heater box made a buzz-click reset sound. Turned car on. Lots of heat. Aha, something to do with the blend doors.

Pulled HVAC codes 41 & 42. Point in this direction.

Took a look under the glovebox. The actuator motor has a white wheel, which, I presume, has little, not visible from below, prongs that engage with slots in other things, actuating them via cam action. My wheel, however, is cocked, so the cam-prong isn't seating well.

Stuck my hand up in there gingerly, couldn't easily move anything. Note to home players, disconnect the battery for this, as the computer will command random movements with the ignition off that could cut your hand.

Checked my cabin air filter-- mice moved in. They made a tiny hole the size of a penny, and made a large nest of "fluff" on top of said filter. New filter is on the way. Assuming more "fluff" found its way down in the works and is possibly jamming the flap, causing an overload on the motor-cam-wheel making it jump from its track.

I need heat, so I unplugged the motor while it's making heat. This buys me time to address things between now and summer cooling season.

Next steps? Prefer not to remove the entire dash, nor discharging & recharging the AC. Can't find good technical info on how to do this on a 4th gen. Any way to vacuum out the vents? Maybe pull the blower motor and go in through there?

 

Well I fixed it.

Removed the glovebox for way better visibility.

There are TWO flaps that this little cam-wheel operates. The one closest to the firewall is the "let heat in" flap. The one closest to the passenger is the recirc/fresh flap. With the cabin filter removed I was able to fiddle with the heat flap and unstick it.

Plugged Techstream in, went to manually controlling the "Air inlet Damper" stepper motor. It only had a range of 220-256. Below a commanded 220 the motor got hung up.

So I manually commanded the motor to somewhere close, I'd say 221 or so, but with a little tension on it. Fiddled with the lever-pin and it popped in.

I still couldn't get it to go to less than 220, but that might be something I was doing wrong. Ended the techstream test and hit the car's recirc button a few times. The wheel is aligned, straight, now and the motor doesn't stall out with a straining noise. Better, the heat flap cycles (more than once!) as the recirc flap cycles. This is a clever implementation by Toyota, requiring one fewer stepper motors, by allowing various (256!) different positions on said flaps.

Here's a horrible youtube video of the flaps in action:

The mouse that got in definitely gets the blame for this. But, it's not something that can be saved with the stock cabin air filter, because the nest was on top of (on the dirty side of) the filter, jamming the flap that's ABOVE it. One would have to put hardware cloth on the cowl input or something similar.

 

You are correct and further experimenting/ driving has shown the problem is not fixed. Such is the issue with intermittent issues. I came to add to my previous post about my misdiagnosing the purposes of the flaps stated.

The properly-found air mix servo seems to rotate smoothly and doesn't make any weird noises, but I'm living in a moment where I have heat. I caught it this morning not rotating, but its reason seems to not be mechanical, so I have to suspect it's something in the software. TS shows all the temp sensors showing appropriate readings, and, besides, the failsafe of "HI" should override those sensors. Lacking any other ideas, I disconnected the 12V battery for a minute. Firing the car back up afterwards, I heard the heater box going through some self-checks.

As you assumed, the fan blows fine and I get plenty of air. It's the car's decision to randomly not let heat into that air that is the issue.

 

Well I think I fixed it with a new 12V battery.

Old one still showed strong on the tester. Used both a capacitance tester and old-school resistive load one.

Swapped batteries with my 21 Prius Prime and the problem went away. Drove it for a full week with multiple cold starts per day.

The issue struck my wife more often than myself, so I tried thinking about what she does differently. She enjoys leaving the headlight switch on, so they shut themselves off automatically after whatever timeout. Also the lights are on, causing a draw, when the car boots up, and the HVAC computer (sometimes) scrambles its brains.

It honestly shouldn't be that bad-- the startup loads on a Prius are way less than a conventional car with a 12 volt starter motor but here we are.

Elected for the East Penn Deka manufactured Group 26R Walmart Value battery for $60 as the permanent replacement. Had to trim a tiny bit off the terminal-side bottom clampy part so it would slide into the retaining slot of the tray, but it's worth it for the additional capacity and money savings over the oddball H4 size.

 

Well, I spoke too soon. Heater failed again on my wife (of course). Code 41. Removed the actuator, part number 063800-9013. Can be done with the dash assembled, but it's unpleasant. You will need a ratcheting right-angle screwdriver, such as 8 Piece Right Angle Screwdriver and you'll need to modify it:

Grind off the 1/4" square socket drive. It will get in your way.

Also, grind down the base end of your philips bit so it sits less flush. This will bring the entire tool down to less than an inch tall, barely enough.

You'll need the glovebox out, and both hands. One will be on the backside of the ratchet to keep it from spinning the wrong way while you're trying to ratchet for another pull.

The "awful" screw came most of the way out with this tool. Finished with needle-nose pliers. 2/10 do not recommend unless you're cheap, desperate, or a masochist. You know who you are.

"New" part (from ebay with a supposed 10k miles) comes in later this week. I bought it based on the parts-throwing assumption that the rheostat in my existing one is flaking out, sending occasional bad data to the computer. Stay tuned.

 

Installed the new part two weeks ago and it seems to be working ok, knocking on wood.

Of note, the "bas***d" screw, I replaced, to make it easier. Took a 1/2" long self tapping screw 1/8" in diameter, found it to be a match for the OE thread size and pitch. Ground the drill head off it, making it about 7/16" long, and a little shorter than stock. This screw has a 1/4" hex head that fit perfectly in my driver (teeny socket wrench) without philips bit fitted, making re-installation significantly more pleasant.

Getting the thing timed was something of a hassle. It has two outputs and a rotation sensor. One "D" shaped output runs a rack & pinion gear that runs a slow "guillotine" that I assume runs the rear heat on/off. Its workings are too stiff to run by hand so I wound up plugging the actuator in, loose, and "booting" the car/ heat until it self-checked and rotated to a favorable position.

 

All right gang, it's still acting up. Next step is to fire the parts cannon at the AC amplifier. Anyone knows where in the car they tucked the thing?

 

Looked up the chilton's manual through my wifes public library card online access. Used a 2016 but it's the same for the entire 4th gen. Pull the little panel under, and in front of the center console, the panel under the dash (that surrounds the OBD connector) and the panel under the dash by the driver's gas pedal. Also remove the gas pedal-- three 10mm headed nuts and a connector.

The HVAC amplifier computer is held in by a single 10mm headed fastener inconveniently facing the firewall, as deep or deeper than the accellerator used to be. Remove that screw, slide it out like a deck of cards, remove three wiring plugs, installation is the reverse of removal.

Fun note, all the numbers matched on my ebay unit, aside from a date code, obviously, and it worked fine for what I need. Of note I got an XLE amplifier (program) and three codes complaining about my (LE) lacking communication with rain-sensing wipers. Said code doesn't interfere with its basic operation of making heat and AC, and doesn't light any lights, so it's a non-issue.

 

Sorry, no pictures, but they would not have been useful anyway-- the clearances down there are tight.