I have a 2004 Toyota Sequoia sr5 model. For the last few months, every time I turn on the A/C, there is this horrible fungus-like smell. It doesn't matter which mode I use ( inside or out), it still smells bad. I got the air filter replaced too, but still the same problem. What could it be and how could I fix it??
The antifreeze levels are also fine- no problem there.

They have an air freshener that you spray directly into the vents and it's supposed to work well, but it is only a "band-aid", have a good mechanic or your local dealership flush the system and recharge. Good luck!

sounds like you have water staying in your evaporator box instead of draining out on to the ground as it should, it will smell moldy cus it is. the drain needs to be cleaned out its under the car passingers fire wall area and is a rubber hose like deal stick a some thing in it and water should run out

I was going to say it's the filter but you had that replaced. I'd take it into the dealer and have then take the hoses apart. May be some stagnant water even maybe something even died in there. friend of mine once found a small dead mouse in the A/C hose.

The Syko Ward

This is a very common problem and there is a solution but it may take a few days to come right. You will not need to buy any cleaning products you just need to operate the A/C in a slightly different way.

What is happening is that condensation that builds up within the A/C is not being given a chance to dry out and the A/C unit within the car is always damp-the dampness is going bad a making the fungus like smell.

The way to correct this and avoid having it happen again needs a little bit of forward planning.

Lets say for example you take 20 minutes to drive to work so you switch the A/C on as soon as you start the car. What you have to do is to anticipate when you will arrive at your destination and switch off the A/C compressor say 3 minutes before you arrive, but leave the A/C fan running all the time to dry out the A/C unit. It doesn't matter if you forget once to do this once in a while, as long as the majority of the time the A/C unit is allowed to dry out.

The car will still be nice and cool to drive in for the last few minutes even with the A/C compressor off.

Hope this helps.