Join Date: Mar 2011
Location: Mid Hudson Valley, NY (USA)
Re: 2005 Sienna LE no front floor heat
In trying to help you and one other person with a rear blower issue, I needed to learn more about how the whole system works. Unfortunately, I’ve only been marginally successful. The information available is marginal at best. It’s treated like a big black box, with limited detail on the internal mechanical parts. Here is what I *think* I know:
The front HVAC system is in two parts, well buried in the dash. Any major servicing will pretty much require gutting the dashboard. Behind the glove compartment is the Blower Assembly fan box with the air input fresh/recirc servo control and door. Behind the center stack is the main heater/AC box with the evaporator, heater core, and output distribution.
The heater/AC box has the temperature blend door(s) – a single servo controlled flap for the manual system (CE/LE), and the split dual servos for the automatic (XLE/LTD). There is also another set of flaps controlled by the Air Outlet servo (also called in some places the mode damper servo). It’s the mode damper / air output system that directs air to the dash vents / dash-floor / floor / floor-defrost / defrost.
The service procedure shows watching the servo motor move over it’s entire range from ‘face’ (dash vents) to defrost. What happens inside the box is not discussed, implying that it’s not intended to be serviced. I went to a dealer parts site, and again, they just have a part number for the box with a price of around $1k, with no details of what’s inside.
My observations: The air outlet / mode damper servo is located on the drivers side high up above where the heater hoses go thru the firewall. There appear to be some linkages that move probably two or three large flaps within the box. Looking in thru the dash vents you can see one of the flaps move to cover over the dash vent outlet when you select beyond dash, going into floor mode. There must be another damper that covers the lower outlet (floor), forcing the air upwards towards the defroster, and one up top that blocks the defroster to force it to the floor. One of those linkages or flaps must be messed up. I would think the servo must be OK, if you are getting dash vent and defroster operation, as it has to move to those extreme positions, and thru the ‘floor’ position. With a light and mirror, or maybe a video camera, you might be able to watch all this stuff move as you cycle the dash switch.
Last thought – at the bottom of the heater box are two plastic ducts that direct the air to the driver and passenger’s feet. They are held up with a single screw on each side. If you remove these, you might be able to look into the bottom of the heater box, much as you can thru the dash vents. Maybe you can get your fingers in there and help the lower flapper (assuming there is one – I think that’s how it works….) move with the mode damper solenoid. This might help you figure out if a linkage came disconnected that can be repaired without tearing it all apart.
I hope some of this makes some sense!!
Current: '15 Sienna Limited Premium (FWD), '14 Subaru Outback, '13 Honda CRV AWD.
Past: '08 Sienna LE (FWD), '02 Subaru Outback, '02 Honda Odyssey EX