Audi A4 Heating Problem: Not Getting Warm (1997)

Hi everyone. I've been having a problem for a while now where the heating in my A4 isn't working properly. Even with a warm engine, the air coming out is only lukewarm at best. I wanted to get to the bottom of this. The entire cooling system has been flushed and refilled. The engine thermostat is also fine. When I read the engine temperature using VAG Com, it's the same as the value shown on the water temperature gauge. However, when I read channel 51 'Engine temperature °C' using the climate control codes with a cold engine, this channel displays '90 degrees'. Which sensor does this channel get the temperature from?

Furthermore, I'm puzzled by channel 53, which displays 'Indication of active electrical outputs: Generator/recirculation valve/water valve.' The water valve always shows '0.' Where is this valve located? Is it inside the unit, near the heat exchanger? Is this valve responsible for the coolant flow through the heating heat exchanger?

Diagnosing the climate control system is a pain. You either need a VAG-Com diagnostic tool, or it's not worth it.

Here's a possible translation:

"It's possible that the interior temperature sensor is reporting incorrect values. It's located on the right side, above the climate control panel, behind the center console. Because a small fan blows air onto it, dust accumulates quickly. This traps heat, and the control unit thinks the car's interior is very warm."

First, remove and clean the sensor. Check the fan for proper operation and replace it if necessary.

However, for this to be done, the entire center console needs to be removed, as the part cannot be accessed from the front.

Diagnosing the Klima (climate control system) is a pain. You either need a VAG-Com diagnostic tool, or it's not worth it.

Here's a possible translation:

'It's possible that the interior temperature sensor is reporting incorrect values. It's located on the right side, above the climate control panel, behind the center console. Because a small fan blows air onto it, dust accumulates quickly. This traps heat, and the control unit thinks the car's interior is very warm.'

First, remove and clean the sensor. Check the fan for proper operation and replace it if necessary.

However, for this to be done, the entire center console needs to be removed, as the part cannot be accessed from the front.

Great, thanks for the tip. Can I also read this sensor using VAG-COM? That way, we would directly see if the problem is caused by the sensor.

Yes, that's fine. I'm not familiar with that specific measuring device, though.

I just tried to read the 'Air Conditioning' control unit using VAG Com. Unfortunately, I can't establish any communication with that control unit. I can easily read all the other control units in the vehicle! Is the control unit definitely defective, or could something else be causing this problem?

It can also be due to a poor interface. The climate control unit is somewhat sensitive to bad interfaces. In particular, cheap USB interfaces or interfaces with optocouplers often don't work.

My serial KKL interface has no problems with my climate control module.

Where did you get your interface from? Did you try it with a dealer before? If it doesn't work with the , then your diagnostic cable to the control unit is broken.

It can also be a bad interface. The KlimaSTG is somewhat sensitive to bad interfaces. In particular, cheap USB interfaces or interfaces with optocouplers often don't work.

My serial KKL interface has no problems with my climate control module.

Where did you get your interface from? Did you try it with a dealer before? If it doesn't work with the , then your diagnostic cable to the control unit is broken.

'That's strange! All the other control units are working fine. I've had this adapter for a while; I think it's from auto-intern. I've never had any problems with it before. I'll get the error codes read.'

Hello!
You're likely dealing with a common problem. Question: Are both hoses coming from the heat exchanger (located to the left of the battery, usually under a corrugated hose) equally warm? If not, then you have the well-known problem of a clogged heat exchanger. Flushing or anything else won't help; it needs to be replaced. This is because the unit is installed vertically, allowing all sorts of debris to settle. The cost of the replacement part is actually reasonable, but the downside is that you have to completely remove the dashboard to replace it.
Best regards,
Dominique.

Hello, I've read about this issue. Both hoses are getting warm, and during a flush last week, the heat exchanger had good water flow with no significant resistance. The vehicle will be brought to the workshop on Wednesday for diagnostics.

D. Briefly: This is also possible, and it's even conceivable that both hoses could be equally warm, yet the heat exchanger is still completely filled with a brownish substance that severely hinders heat transfer! Before proceeding, it's advisable to check if the servo motor (for the climate control) is disconnected or if the cable (for manual temperature regulation) has come loose.

@T3surfer:
Of the 3 patients with this problem I've seen so far, none of them had any flow through the radiator. It's possible that if there's still 1 or 2 cm of space, there might be some flow, but no heat can be transferred to the air.
Okay, let's check the flaps with the tester. If something is moving, it's probably the heat exchanger. There's no valve, so it can't be that.

Greetings,
Dominique.

"D.Kurz is right again; I've experienced something similar once, although it almost completely blocked the system. In that case, the heating was freezing cold. The other outlets had a light to full flow, but were only moderately warm to lukewarm. Yes, there are no water valves for this heat exchanger. Oh dear, I guess I'll have to remove the dashboard..."

The problem has been found; the water cooler had a small leak (not the heater cooler!). This prevented any pressure from building up in the system. A new cooler has been installed, and the heater is working again. Thank you for your help.

I was secretly hoping it was a ZKD reference while I was reading, thanks for clarifying!