Toyota Sienna Forum - siennachat.com banner

2009-Rear vents only blowing cold air

3727 Views 5 Replies 2 Participants Last post by  pethelman
2
Hi all,

I'm having a problem with the rear air being stuck on a/c- the blower works just fine. I dismantled the right rear interior paneling and located what I believe to be two motors (not sure which is the blend door actuator). The motor on top seems to be working.

I also see a door, which is made of a thin but sturdy plastic. I think it is supposed to move in order to control the balance of cold/hot air by blocking either the a/c core or heater core. See attached photos. This door does not move by hand or when I adjust the thermostat on the rear vent controls- I'm not sure of the designed operation of this either. There is a motor that operates this door that is mounted in a very inconvenient position on the inner side between the blower assembly and the inside of the rear quarter panel. Do you think the motor that operates this door is my culprit? This Youtube video shows it better, except the plastic door doesn't move at all.


43818



43819
See less See more
1 - 6 of 6 Posts
Ok, so the motor on the top, as you have noted, is the water control valve for the heater core. As you move the temperature toward warming the interior, this valve will proportionately allow more hot water to flow through the heater core. You should be able to run the temp control (for the rear) up to MAX and down to MIN quickly and see this actuator move a good bit. The other servo motor is simply controlling the air-diverter door and it does this purely based on the requested "mode." If you alternate between air requested at the floor and through the vents (regardless of the temperature set point), you should see this door open and close. And yes, getting to that motor really might require partially loosening the entire assembly, or you might be able to get at it with some ratcheting screwdriver tips and a mirror? I remember thinking that replacing it would be a real bear. I would definitely want to rule out everything else first though and make sure that the correct control signals were actually showing up at the servo. Sorry I don't have a good method to give you for doing this other than to consult the FSM and break out the voltmeter.
See less See more
Ok, so the motor on the top, as you have noted, is the water control valve for the heater core. As you move the temperature toward warming the interior, this valve will proportionately allow more hot water to flow through the heater core. You should be able to run the temp control (for the rear) up to MAX and down to MIN quickly and see this actuator move a good bit. The other servo motor is simply controlling the air-diverter door and it does this purely based on the requested "mode." If you alternate between air requested at the floor and through the vents (regardless of the temperature set point), you should see this door open and close. And yes, getting to that motor really might require partially loosening the entire assembly, or you might be able to get at it with some ratcheting screwdriver tips and a mirror? I remember thinking that replacing it would be a real bear. I would definitely want to rule out everything else first though and make sure that the correct control signals were actually showing up at the servo. Sorry I don't have a good method to give you for doing this other than to consult the FSM and break out the voltmeter.
Thank you for the very detailed response- now I can put 2 and 2 together regarding the air diverter door and motor simply being used to direct the flow of air to the floor versus the overhead vents.

I removed the top motor and disassembled the casing to make sure the guts were ok- they were. I then changed the rear temperature dial and watched as the motor shaft rotated just fine. I can't tell if it's actually going full motion but appears to be. So when that motor closes the valve to the water control valve for the heater core, is that when the air conditioning should take over? Or is there another valve or mechanism I need to look at that controls the a/c? If that's the only motor, maybe me opening up the housing unjammed the gears somehow and now the system will work.

Thanks again
So, did you ever get the servo on the back side of the housing to slide that door open and closed?

So here’s how it works in a nutshell. The water control valve diverts hot water into or bypasses the heater core as needed depending on the demanded temp. At any point if you turn on the compressor, the “A/C” is working and the evaporator coil in the rear box will start getting cold. When you demand heat at the same time that the compressor is running, you literally now have a heater core and evaporator coil “fighting” each other. The heater core, however, is able to overcome the cooling factor, and in fact, you WANT this to happen because the cold coils are now simply acting as a dehumidifier, which for a big van in the winter, is a very important function.

If your diverter door control isn’t working, you can still get hot or cold from the rear, it’s just that one or the other is going to be coming out from a non-optimal vent location.

So, yes, if you demand cold temps, the hot water will bypass the heater core and the evaporator will “win” the battle (assuming the compressor is running).
See less See more
So, did you ever get the servo on the back side of the housing to slide that door open and closed?

So here’s how it works in a nutshell. The water control valve diverts hot water into or bypasses the heater core as needed depending on the demanded temp. At any point if you turn on the compressor, the “A/C” is working and the evaporator coil in the rear box will start getting cold. When you demand heat at the same time that the compressor is running, you literally now have a heater core and evaporator coil “fighting” each other. The heater core, however, is able to overcome the cooling factor, and in fact, you WANT this to happen because the cold coils are now simply acting as a dehumidifier, which for a big van in the winter, is a very important function.

If your diverter door control isn’t working, you can still get hot or cold from the rear, it’s just that one or the other is going to be coming out from a non-optimal vent location.

So, yes, if you demand cold temps, the hot water will bypass the heater core and the evaporator will “win” the battle (assuming the compressor is running).

Ok understood about the scenario where heat might not be working. So essentially, that water control valve should be in the closed position when I am only requesting A/C? If I am still getting hot air, that means either the coils aren't getting cold (they are) or the water control valve is not closing fully or at all (bad motor?).

The vent diverter door is working properly, I was confused initially as to the function of that motor.

Thanks
Yes, if you're requesting max cooling then the water control valve should be in a position to essentially be shunting (bypassing) the heater core, and you should have little to no heat in the core. I can't be 100% certain that the valve is functioning as a bypass vs. simply a shut-off, but it does seem like both the supply and return lines would get hot, even if I wasn't asking for heat, which leads me to believe that the valve is creating a hot water "loop" (bypassing) the core, when demanding cold.

I also remember when I had mine apart that the only thing making the servo unique for the water control valve was the shape of the "keyed" shaft that was actually turning the valve. Basically just a nylon shaft with a flat on one side to engage the valve. I was able to find an Alan wrench that fit tightly in the valve and was able to turn the valve by hand, but it was quite stiff. Not sure what they should feel like when new, but at least mine was quite stiff, and is still functioning fine. You probably already have when you had it apart, but you might just check the condition of the shaft on the servo and make sure it hasn't been compromised in some what that would prevent it from fitting well. In other words, while assembled, make sure that it's actually turning the valve? Will be interested to know what you find.
See less See more
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top