rockdoc

Board

Has anyone had a problem your heater staying on even though I have the temperature set to low? I turned up the heat for a few minutes to warm up the cab and then turned it down. The air out of the vents stayed hot. Even on the next day (today) when I went out for a ride. (I'm glad I have a cab... just kept the top down and all of the vents closed) I checked all of the fuses and connections to the heater manifold.

I checked all of the past posts and most of the CCU issues were concerning the air conditioning. Should I take it into the dealer to have it hammered? Is there a simplier way to check this? Is there a way to disable it until I can get if fixed?

TIA

mike cap

Rock Doc,

You problem is either in the CCU or one (or both) of the flapper valves that control hot air from the engine.

Is the heat coming out of the under dash vents on the RH and LH sides as well and at equal temperature? If one side stays hot and the other cold or cool, most likely you have a defective temperature sensor on one side. These temperature sensors and flapper valves are located under the RH and LH kick panels in the footwells.

If air from BOTH the RH and LH under dash heating vents stays hot no matter how you adjust the CCU, then that may be the culprit. Ouch.

I just sorted out a problem similar, but my squawk was hot on one side and cold on the other. But I do understand the system better now.

Post back if you have more information or call me at the office. 800-333-0519 x106.

Robin 993DX

Mike is right ON with his diagnostic.

The nature of the 911 air cooled engine heating system is that heat is constantly being pumped from the engine area through the heat exchanger to the cabin of the car as long as the engine is running regardless of the HVAC temperature setting.

If you just have the key on ACC position with the temperature **** turned up you can hear the electric fan working from the engine department to force the hot air through.

The problem with this type of design is that the hot air must be some how block when the heat is not turned on, or else you get nothing but HOT AIR "pun intended" in the cabin of the car.

There are two servo controlled valve that allocate different amount of the hot air through on each side of the footwell area. That's why it would be important to find out which side of the vents have hot air coming through.

I suffered the same exact heat problem not too long ago after moving to FLORIDA durign the middle of summer. I discovered that one of the servo was stuck open. It is easy to diagnose the problem as with the key turned on and temperature set to coldest setting both of the servo valves should be closed. My problem turned out to be a stuck servo motor, I took the servo motor apart and fixed the problem by hitting it with an Irish screw driver (hammer).

Below are some pictures of the servo and the heater ducts. In case you wonder why the fail safe is always in the open position.... The German's logic was that it would be better to have heat always come into the cabin in case if there was a failure with the servo motor, better not to freeze to death than heat...

Robin 993DX

LOL!

Sorry, it was suppose to be "ON", not "NO"

mike cap

Robin,

Do you have photos of EVERY part of you car in various stages of disassembly?? And on file for instant access?? You're amazing....

rockdoc

Mike and Robin: Thanks for your help with diagnostics. The pictures are extremely helpful (I agree with Mike about the amazing amount of 993 data you have). I will check the the underdash vents tonight to see if it is equal on both sides and get back to everyone. The center dash vent the one that I have focused on because of the hot air blasting in my face. The dash side vent (driver's side) is also blowing hot air. Just a quick question about checking for a stuck servo. Should I have the car running or just turned to Aux?

Kim - I spell checked! :-)


Thanks to all for your help.

Robin 993DX

Rockdoc,

All you need to check for the servo position is to have the key turned on at ACC position. (One position right before starter engages)

Mike, I guess I have a lot of pictures because my car breaks down a lot.....

:P

Thanks

rockdoc

I took the car out this afternoon and the heat was coming mostly from the passenger side. However, as the car got hotter, the heat was coming from both sides.
Robin, in testing the servo position, I take it I have to take the servos out when look to see if it is closed or opened like you have in your pictures. Right? And may I ask where you used your Irish Screwdriver? I may need it for my head later! :-)

rockdoc

Thanks for your advice Robin and Mike. You hit the problem right on the nose. Right side was stuck open. Took the servo apart and gave it a few taps. I reconnected and it closed when I turned on the power. I hopefully it is good to go for a long time. Thank you for saving me time and money! Now I'm ready to tackle changing the headlights.

chris walrod

Lets turn this into a game of 'Lets Stump Robin'

The game is easy, we will post various topics and see if we can stumble upon one in which Robin DOESN'T have a picture of.....J/K

Rennlist saves yet another dealer visit!!!!!!!!

bschilt

The AC continues to be a hot topic. One of the things I have not seen any posts on are the vents in the rear, under each window behind the seats.

None of the CCU settings in my car seem to control blowing air out of those

Any insights on how these are part of the overall heating and ventilation system?

Is air flowing through them into the cabin, or is maybe the purpose to have air pressure (from open windows or the heater) flow to the outside ?

Felix

They vent cabin air to the outside otherwise the cliamte control system would be trying to blow air into a closed chamber.

bschilt

Where do they come outside? The wheel wells? Is there a flap or so that can be congested or stuck?


I think there is more hot air coming in through them than that it helps with the air circulation

Edward

Given his track record, this will be a verrry long game!

And yes, RL saves us again. But only because of the fine folks here that make this community like precious few others out there. Is this a great place or what

Edward

GabiOsz

Can i just re-iterate how much i love this place!?

I was driving my girlfriend to the airport and my driver's side heater was stuck on full. By the time i got home I was sweaty to say the least, and less than pleased with my 17 year old 993.

Such good (illustrated) guidance, and I managed to fix this myself, without the displeasure of being charged a small fortune for experimentation and "diagnosis" from my local stealer.