Any ideas on how to remove "idiot proofing" in my van's climate control?

[MrPlow]

First Gen Toyota Sienna. Good van! Although, the climate system has been made stupid by idiot-proofing several features.

Here's the problem. When the control knob is set to defrost, it automatically turns on the AC system and opens the recirc vent. I would like the option to turn on the defrost windshield blower ports, but NOT open up the recirc vent and turn on AC. It's just not needed when a little warm air is all that it takes to keep the glass from fogging up. I don't like the idea of wasting my AC system and gas when it is not needed. I also prefer to have the van on recirculate mode when in traffic or behind stinky diesel monster trucks rolling coal everywhere.

Ideally, the system should just allow for changing the blower vents without automatically opening the recirc and turning on AC. If I want a combo, I can just hit the buttons I want for that combo. The way Toyota idiot-proofed the system makes it less ideal for people who know how to press two buttons instead of just turning a dial.

I was thinking of taking the dash apart and either disconnecting the AC wire going to the relay or cutting it, and also seeing if I can dismantle the mechanism that opens the recirc. I would leave the AC and recirc buttons alone and keep them operational. Only the automatic mechanism in the vent dial needs to be modified.

Any thoughts on whether this would be the best plan of attack? Any ideas on doing this without removing the dash? It's not really that hard, but is more involved than other dashes I have taken apart.

Here's the setup.

 

[oldhp]

The AC comes on in defrost mode to help de-humidify cabin air. By allowing the AC compressor to come on in the winter it keeps the seals soft and the system coated with the oil used as a sealer. I would just leave it alone.

 

[MrPlow]

The AC comes on in defrost mode to help de-humidify cabin air. By allowing the AC compressor to come on in the winter it keeps the seals soft and the system coated with the oil used as a sealer. I would just leave it alone.

I know that, but it would be nice to have the option to do what I want and not have AC on. It makes the air colder even when turned to max heat, and for many days, it's just overkill. On bad days, I can just turn it on by pressing the AC button.

 

[kschachn]

How do you know the recirculate is reversed when in defrost mode? My old Sienna does not do that.

 

[MrPlow]

How do you know the recirculate is reversed when in defrost mode? My old Sienna does not do that.

It pops the recirc button out and opens the vent. I can hear it opening when this is done. In the photo, I pushed the recirc button back in to close it again. With the AC though, I have no option from these controls to turn it off when in the defrost vent modes. I would prefer to not have to switch it back to recirc every time I switch to defrost, as the mechanism is probably as involved as getting to the heater core if/when it goes out.

Van full of wet people and a cold winter day? Open recirc and AC on full blast to get moisture out. For a normal day where the only moisture is from my breath and sweating fogging up the glass a little, a tiny bit of warm air without AC is more than enough, even with recirc closed.

 

[Jetronic]

Can't help you there... If I chose defrost mine does the same, but i can also aim the air on the windows without pushing defrost and then I can choose whatever I want, recirc or not, ac or not, auto blower speed or not, any temp I want.

If you don't want to use AC in winter disconnect the AC clutch or maybe the ac pressure sensor. You could wire a switch to do it from inside the car aswell

 

[mk378]

Easiest way to disable A/C is to unplug the compressor or pull the compressor relay, which is usually in the fuse box under the hood. Try that and see how you like it. In 45 F rainy weather the dehumidify effect helps a lot. Below freezing the compressor normally doesn't run because of low refrigerant pressure.

As others noted, the recirculate button probably still works. Running recirc damp air will lead to fogging. You can put some heat on the windshield but the other windows will fog up.

 

[Astro14]

Turning on the AC when defrost is selected isn’t new.

My 1977 Oldsmobile did the same thing.

So, I don’t know when you could last get a car that works the way you want.

Perhaps something from the 1960s?

 

[MrPlow]

Yeah, I guess I should clarify. I WANT the AC to be optional, not fully disabled. It's nice to have when there is a lot of moisture to clear quickly. For the vast majority of driving in traffic and around town, it's overkill. I also hate the idea of running the AC compressor on cold mornings when I'm trying to heat up the windshield to melt ice. AC runs the cold engine harder and hurts the temp of the air hitting the glass.

 

[kschachn]

It pops the recirc button out and opens the vent. I can hear it opening when this is done. In the photo, I pushed the recirc button back in to close it again. With the AC though, I have no option from these controls to turn it off when in the defrost vent modes. I would prefer to not have to switch it back to recirc every time I switch to defrost, as the mechanism is probably as involved as getting to the heater core if/when it goes out.

Interesting that must have been a later implementation.

 

[Jetronic]

Yeah, I guess I should clarify. I WANT the AC to be optional, not fully disabled. It's nice to have when there is a lot of moisture to clear quickly. For the vast majority of driving in traffic and around town, it's overkill. I also hate the idea of running the AC compressor on cold mornings when I'm trying to heat up the windshield to melt ice. AC runs the cold engine harder and hurts the temp of the air hitting the glass.

2 wires and a switch inside the car it is....

 

[MrPlow]

Interesting that must have been a later implementation.

Yup. The 2000-2003 (or whatever years got upgraded to VVT-I) Sienna models of the first gen had different climate systems. The 1999 model has more user control over the system like what I find in the old Toyota pickups and the 2004 gen 4Runners.

I probably would have preferred the older version, but the VVT-I models have more driver knee room and the one I got came with traction control and skid control.

 

[MrPlow]

2 wires and a switch inside the car it is....

I figured. But thought I would ask if anyone had better ideas. I hate taking dashes apart. It always feels like I'm going to break something, and they never seem to go back together exactly as they should. LOL

 

[Jetronic]

no need for the dash to come apart for this

 

[mk378]

Something that old probably has discrete wire controls rather than running bits on a CAN bus. Get a schematic of the car and find if there is a wire from the HVAC control head to the ECU making A/C request. Interrupt that wire.

 

[Jetronic]

exactly, and if it's in a big bundle you can look for the AC relay and interrupt there, or worst case do it at the compressor itself

 

[ripcord]

One thing to consider is that it your AC system will last longer if it is used regularly. I wouldn't worry about it, myself.

 

[lenjack]

Seals get lubed when in automatic mode. This reduces the chances of system leakage as vehicle ages. Leave it be.

 

[MrPlow]

Welp, I will make sure to turn on the AC from time to time all year round. That's excellent advice. It doesn't need to be one the whole time I am driving though. And it absolutely doesn't need to be on during a cold start looking to melt windshield ice.

 

[CKN]

Unbelievable...............................