simonsun347

Hi everyone,

I have a 1999 d2, having an AC problem where the heat will not work. The fan blows, but cold air comes out no matter what temperature I set it to (even on HIGH) and how fast it's blowing (the vertical bars reading).

All buttons work. Coolant temp is right-on.

If i put it on ECON mode, left side blows warm air, right side still stone cold.

Defrost mode is also somewhat warm on left side, right side stone cold.

Did a vagcom scan with VCDS lite 1.1 and ebay cable, address 08 HVAC unit returns readings (so i assume it recognized it something is wrong, because no other modules returns anything, in other words everything else is fine.) but will not give any fault codes. I believe a window popped up saying something like this function is restricted blahblah, and this happens both when i do auto-scan and just address08 HVAC unit scan.

I scanned other modules fine (01 engine had a problem with MAF-fixed, 03 ABS had a problem with sensor-fixed) so I'm pretty sure the cable can connect fine.

So do i need the full version (the 99$ version to run any HVAC scans? anyone knows? is HVAC fault codes special or blocked?)

More importantly what's causing the symptoms?

Thanks guys any help is appreciated.

silverd2

Unlike most other Audi's & VW's, which have a constant unrestricted flow of hot coolant through the heater core which is only regulated with temp flaps in the cabin, the D2 has a pump/valve unit next to the brake booster under the hood.

I'm no expert at troubleshooting the unit, but know a few things that may help narrow down your problem. You have 2 heater cores (left and right)...the flow to each is controlled by the solenoid valves in that unit...the pump in the unit is mainly for the restore feature on your climate control head (temporary heat with engine and key off).

Is there any evidence that stop-leak was ever used or wrong coolants mixed (brown sludge in coolant, maybe settled on the bottom of the reservoir)? Either of these can (and have with past posters) clogged the control valves in the pump/valve unit.

Have you felt coolant in/coolant out temps on heater hoses? ...a good indication that coolant is flowing freely through the heater cores?

^^ Just a couple of thoughts about other causes (that may not show on a vagcom scan), besides in-cabin controls.

simonsun347

Hi Silverd2,

Thanks for the reply. I will check per your suggestion next week when I have my car back and update here. My friend is taking my car for the weekend trip. (with no heat, new england weather, but fortunately the heated seats are working).

To your question, there is a minor leak in the cooling system, i still don't know where. I just keep topping it off. I've never used stopleak or anything like that, but i did use something (green? orange?) that my friend uses for his VW jetta that is non-G12 once. I'm not seeing any residual in the coolant tank itself, will check valve and heater core.

Do you have any idea as for the vagcom piece? is it truly showing no code or is it just because i have the VCDS lite shareware version so I'm not getting them?

Thank you.

silverd2

Even the free lite version of VCDS and cheap OBD cable (what I use) will read any fault that the full version can, so long as you can open that module. For instance, recently I read HVAC codes related to my intake (recirc) flaps...sure enough, the flap motor wasn't working all the time to open and close this.

ANY other coolant mixed with G12, especially orange or green (no matter what the label says) will eventually form brown sludge somewhere in your system...it may or may not show up in the reservoir...some other cars it will clog the heater core first (narrowest passages), before showing anywhere else.

We've had my wife's Allroad almost 2 years and just recently the heater core clogged with sludge (easy hoses-off back flush cleared it)...only then did I notice the same telltale sludge around the level switch in the reservoir (cleaned that out too). The past owner/mechanic must have topped with something orange or green in the past...compared side by side I found the coolant has a slight orange cast next to the coolant in my D2. Total chemical flush is in the plans soon for the Allroad.

simonsun347

So if I'm getting message output for that module but no fault code...there's gotta be something wrong with it but vagcom can't read? or there's simply no response the the climate box is broken?

I will check for any blockage in the cooling system, but the fact that one side is dead cold i'm thinking it's more mechanical?

What do you mean by a total chemical flush? I only know if you unscrew the drain hole and pour hot water into it to flush the system.

Thanks.