Why isn't my heater actually heating?

Regarding the a/c button, if you have the selector on defrost, the a/c should stay on. If you turn the a/c off, and turn the selector to one of the other settings (such as floor or vents), does the a/c turn off then?

Regarding the heater temperature, if the fan is blowing normally, it is likely either the thermostat is stuck open or the heater core is clogged, either internally (not allowing the coolant to flow through it properly) or externally (not allowing the moving air to pull the heat off of it properly). Does the car warm up to its normal operating temperature? If you have a temperature gauge, check to verify that it warms up to the middle of the normal range. If it does not, chance are good your thermostat is stuck open. If it does, then the thermostat is probably working correctly, and it is more likely that the problem is with the heater core.

There is a remarkably common problem with Jetta heater boxes. I have discovered it in my own 2003. When we purchased the car used we noticed a flurry of foam from the vents when heat or A/C was turned on, and thought not much of it. I just figured it was probably a lining of some vent that had worn over time. Since that time...with extremely poor heater performance my research led me to discover that the vent doors, once sandwiched with foam deteriorate over time and leave stamped metal doors with huge holes punched in them. These now obvious holes leave hot air to mix with outside air, and never divert hot air as they would if they were solid.

Since a pic...and a very helpful video is worth more than a thousand of my words...check this out if you discover all else recommended has failed. I believe you would want to take a look at this before you go replacing the heater core.

http://www.youtube.com/watch?v=4c1cjA-y7...

I know this problem has an old date stamp but the problem is the air doors that direct the air flow to the A/C evaporator or the heater core have lost the foam seal on their sides. This also happens on the defrost/ floor door.

The job to have a auto shop reclaim all the freon in the A/C system and drain the coolant from the engine. Then disconnect the heater hoses and the A/C lines and Expansion valve from the evaporator. Then the time consuming fix this is to remove the dash and the heater/A/C unit and open it to reveal the doors. You can replace the seal by first cleaning off all that remains of the old seals and cutting out need seals from dinner plate protector sleeves found in moving departments of hardware stores. Cut it to the right size so the doors is sealed but not prevented from moving or sealing due to the new seal size. Using 3M spray tack, spray on one side of the new seal and after masking off the metal door, the one side of each door at a time with an even light coat. Let it dry 3 to 5 minutes and put the seal in place with "one shot" placement.

The age of car I would recommend that the heater core be replaced at the same time.

The car is worth it if it isn't rusted out. I have done several including to of mine. An auto shop will charge for 12+ hours of labor but a friend who likes to work on challenges could handle all but reclaiming of the freon.

Parts cost is less than $30.00 provided your anti-freeze is good and nothing gets broken.

Some good background music and a few cups of coffee always help the job go better!

One day I noticed the heater would not produce any heat, not matter what the position of the thermostat.

It turned out the thermostat cable tied to the knob was disconnected behind the console.

Apparently this is a fairly common problem with this car and garages love it because it can be made to look like an expensive repair, such as A/C replacement, etc.

Instead I fixed it with just a couple screwdrivers and a little bit of time.

There's a lot of plastic covers to remove but in the end, I could find the connector that was indeed disconnected. It plugs up, so I suspect after 15 years, it slowly nudged itself down via gravity and vibrations.

Even though it's somewhat difficult to access with your fingers, I was able to plug it back up.

Works like a charm now!

Long story short, I compiled the few videos that helped me remove the plastic covers in order to get access to the console. Counter-intuitively, you have to start from the back seat to remove the center console and work your way towards the front.

Then follow the cable that connects the thermostat and the other end might be dislodged just enough that it cannot control the heater anymore.

https://youtu.be/7mR6mH3ZlOI

https://youtu.be/5Od5pg1KxLw

https://youtu.be/K_k5MFC2wMQ

heater core 100 % thats all it could be

I’m pretty sure the previous owner blocked off your coolant hose return line, they do this to bypass coolant after a hose bust or (not very common) your heater core is leaking.