Nicolito

I have a heater problem on my 911 996 1999 C4 and have search for similar problems in the forum without finding the exact same problems. Trying to start a new post:

My heater sometimes only blow cold air and when selecting Defrost (all air on front window) it only blows cold air into coupé.
Sometimes when the car gets warm I can restart and get the Defrost to work and blow warm air on front window and after that I can change between Auto and Defrost without problems.
Sometimes but rarely all works perfect from beginning with good heat.

I have noticed small flakes of foam coming out of the vent, but not much.
I have looked at the servo on passenger side (where you have your feet) which I think is moving the flap to get air to front window and that doesn't move when I can't get defrost on front window but it is moving when everything works.

Can the problem be:
- foam on flaps need to be repaired?
- thermostat problem?
- HVAC electric problem?
- servo problem?

Hope to get some guidance here!

Many thanks
Nic

De Jeeper

Probably the foam issue but also could be a clogged heater core. They r not hard to change or even flush. Its is installed from the frunk behind the battery. I guess it could also be a t-stat stuck open but i would start by getting a visual on the vents

motoo344

If its because of the foam then its a relatively simple DIY if you don't mind cutting one piece of plastic. The flap with the foam can be accessed from under the windshield cowl, there is a plastic piece you must cut to take the flap out. The two hardest parts are cutting the plastic and then taking off the flap from under the dash. The plastic is hard to cut because its a tight space, with a Dremel tool it might be easier, I used a saw blade by hand and wiggled it back and forth. The flap from underneath is just awkward because you have to get in upside down but it isn't hard to access. My heat blows real hot now.

DBJoe996

It is strange that sometimes it works right and sometimes not. A good way to check if it is the flaps and foam is to block the fresh air intake filter. Remove the pollen filter, cover it with a plastic bag or saran wrap, reinstall and see how things work. That essentially blocks the fresh air intake (cold air from outside). Put your HVAC on recirc (just moving around the cabin air) and see how it works.

ZuffenZeus

Nic,

Try these steps...

Go for a drive in the car and get it warmed up to the normal 180˚F temp setting. Once the car is warmed up, follow these simple steps and report back:

1. Turn the temperature setting on the AC control unit to "HI" by pressing the + button (GREEN arrow) until it's shown.

2. Next, turn the fan speed (YELLOW arrow) to the midpoint or higher

3. Last, engage the recirculate air button (RED arrow)


This should produce heat in the cabin in spite of the blend door problem with these cars.

Eurocarguy911

Excellent work around!

details

I'm curious -- will this produce as much heat as fixing the problem?

I've already gone in through the center stack on my car and sealed the holes with metal tape. But my curiosity is raised since both doors have holes in them. I was unaware that you could do this until AFTER I fixed my car!

DBJoe996

I am absolutely amazed. My posts mean nothing. There is no problem. The SOLUTION is pushing the right buttons on the HVAC controls. Absolutely amazing. I am truly floored. Seriously considering not posting anything anymore, no helpful hints, no suggestions, no insight. Why bother?

Nicolito

Thanks for all comments and tips. I haven't had time to go to the car and try it out yet but hopefully I will this weekend and I will respond back after that!!
Many thanks!
Nic

ZuffenZeus

Both of my 996 cars had the unfortunate blend door problem which of course affects the heat output. My workaround (noted above) worked great for me on both cars during the winter. Of course, solving the problem would mean cutting open the blower enclosure through the center console and patching the holes in the blend doors. However, the workaround did the job to produce lots of heat in the cabin and so I didn't bother with cutting open the blower.

Nicolito

Snowy and cold in Stockholm today so excellent conditions to test the heater and defrost.

Tried out the tip from "b3freak" today but no luck for me. Still only cold air coming out. Drove for about 20 minutes, made a pit stop for food and when I started up again the heater worked perfectly with lots of warm air coming out and possible to get air flow on front window.

I will try out the tip from "DBJoe996" to see if that help.

My concerns:
Why is only cold air coming out? (thermostat / temp sensor in cabin?)
Why can't I get the cold air to flow on front window? (servo problem?)

Nic

DBJoe996

Hmmm, there is a cabin (inside) temperature sensor on the passenger side of the dash. Could be out of whack. Also, make sure the ambient air temperature sensor in the front bumper hasn't gotten knocked out of place and is now behind the front bumper. There is a little holder it resides in in the front bumper. Next, it could be a stuck thermostat...so how does your temperature gauge on the dash read? Another source of cosmic problems is the electrical portion of the ignition switch, but in this case I don't think it applies. Overall, how does the HVAC system run? Fan and temp variable on the display? Could be the HVAC controls are out of whack as well. One last thing, manually check your coolant level.

ZuffenZeus

^^^ I agree with Joe's suggestion.

I can't help but have a flashback to a guy we were helping with the same problem here on Rennlist. He also tried the workaround but didn't help the situation with no heat output. Obviously something else was the culprit. Come to find out, his heater core was malfunctioning from a blockage. Pulled the old one out and replaced with another OEM, flushed the system, and it fixed the problem.

dcdrechsel

Could be heat control flap ( also know as blend door ) motor on it's way out .Not hard to check -remove foam panel under dash in passenger foot well .Motor is left of fan and will activate with temp changes with ignition on .

Nicolito

Today tried the tip covering the pollen filter with saran plastic wrap and HVAC on recirc but still no heat and the air can't be directed to front window.
Also topped up coolant fluid which was a few cm too low.
Unfortunately no luck!

Noticed the outside temp sensor in front bumber hanging loose but seems connected, will open up and have a closer look.
Is there a way to see if inside cabin temp sensor works?

The HVAC seems to work well when I get the heat, I can change and adjust as normal so it seems ok.

I opened up and looked at the heat control flap motor (what I called servo earlier) located at passenger foot well and that is not moving when it heat/defrost doesn't work, but when heat/defrost works it is moving when and I change to Defrost.
Does that motor control the air flow going up on front window or controlling heat coming into the cabin?

// Nic