2004 Toyota Sienna FOGGING of WINDOWS WHEN USING HEAT

KIB

MEMBER
2004 TOYOTA SIENNA
6 CYL
AWD
AUTOMATIC
55,000 MILES

I am having a problem with all the windows completely fogging up when I use the heat in the dash position (not as bad when I use floor only position). It gets so bad tht I can not see and am forced to keep the defroster on which trips the heat mode to go to floor board positon. I can not use the heat in the Dash vent position with out this happening. I use the heat in the recirculate positon not the fresh air mode. What is causing this? I took it in to Toyota and they told me they checked the presure in the heater core to see if there was a leak. They pressurized it for 2 hours and they said it held at 12 pounds without moving. They also said no leak in the lines. What should I do next?

5 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

There is a moisture problem somewhere. IF it isn't the heater core then there is moisture getting into the HVAC unit somehow. Maybe a water leak?

Have you changed the cabin air filter? It is located behind the glove box? I can provide directions if need be.

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Friday, April 18th, 2008 AT 6:16 PM

KIB

MEMBER
3 POSTS

Thanks for answering. I just had them to replace the cabin filter with this service. It has been changed once before around 30,000 miles. Could that have been affecting the build up of condensation inside?
Also, I was told that the radiator cap was leaking a little. They replaced the cap as well. The fluid was only down a little. Could that have been the problem or contributed to it?

Last year the Air conditionor broke in the summer and only sent out hot air through the system when AC was turned on. I was told when they fixed it that it was the compessor. They fixed that problem however since that time when the weather became cold I started having the condensation buid up on the windows with heat use. Could this be related in any way?
If it is a leak where would the leak be coming from and going to? Would it get wet inside the car at all? Thanks for your help.

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Friday, April 18th, 2008 AT 8:06 PM

SERVICE WRITER

MECHANIC
9,123 POSTS

Condensation has to be coming from somewhere where there is moisture getting into the air duct somehow. IF it is a small enough leak it may not show on the carpet.

Do you park in an area that debris such as leaves can clog up the wiper drain?

Radiator cap wouldn't be related, but do you ever have to add antifreeze? Actually is the moisture on the window greasy at all? Or does it purely seem like water moisture?

Not sure if there would be a tie into the a/c repair, there is an evaporator core in the HVAC unit. Try running the A/C on you next ride. When you get to the destination, see if there is any water dripping underneath your car while it's running. Maybe the evap drain is plugged and holding moisture?

On the cabin air filter, I had thought maybe it was retaining mostiure and acting like a paper towel hold moisture until you ran the heat where it we dispurse the mositure and allow it to soak up more afterwards.

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Saturday, April 19th, 2008 AT 5:31 AM

KIB

MEMBER
3 POSTS

Thanks for answering! Yes sometimes the windows are somewhat greasy like. It is not extreme though. I have never had to add antifreeze between services. The radiator was replaced once due to recall by Toyota. That was several years ago.

I do park under the shade of a tree and yes leaves do fall into the window washer area.

The filter could be getting wet however Toyota who just replaced it for me didn't say anything about it having moisture in it.

I do notice when I am getting a car wash that the smell of the detergent used in the car wash comes into the car through the vents very strongly after a and during a car wash. It is really an obnoxious smell.

The car does release water under the car after using the AC when I park. I've noticed a lot of water.

Any more suggestions or advise would be much appreciated.

Thanks

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Monday, April 21st, 2008 AT 2:22 PM

SERVICE WRITER

MECHANIC
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Check the drain in the wiper transmission area and make sure there is nothing preventing rainwater or car washes from draining.

The a/c drain is not blocked as evidenced by the water dripping while a/c is used.

Typically a greasy film is caused by leaking coolant.