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No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin

Bobot1994 17331 34
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Why is the cabin heater in an Audi A4 B5 blowing cold air even though the engine reaches 90°C and the heater hoses are warm?

If the heater hoses are warm but the cabin still blows cold air, the most likely fault is the heater box flaps/foam seals or the heater unit itself, not the engine temperature reading [#19726517][#19727401][#19729167][#20370772] In that case, the usual fix is to remove the heater assembly and regenerate the circulation control flaps with new sponge sealing material [#19726517][#19727401][#20370772] If the upper radiator hose is hot and the lower one stays cold, and the fan does not switch on, also check the thermostat and the head gasket because combustion gases can create an air pocket in the cooling system and stop proper heating/cooling [#16859767][#16859820] A CO2 head-gasket leak tester was suggested as the next diagnostic step [#16859958] Also verify the temperature knob/cable is moving correctly, since one reply noted the cable may be burned out or disconnected [#16855901]
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  • #31 20396292
    michal8819
    Level 11  
    Under the ECU are the ones on the left next to the fuses?

    Added after 1 [minutes]:

    I unscrewed the 2 on the left side and one on the right for the 16 key but somehow it still sits stiffly.
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  • #32 20396330
    Ireneo
    Level 42  
    Under the ecu for the cross and from the bottom next to the ecu for the key 10. Sixteen and one from the pedal bracket on the imbus. See the rest if I don't remember
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  • #33 20396359
    michal8819
    Level 11  
    Thanks for the info.

    Added after 51 [minutes]:

    And one more thing, when I pulled out the board, I tore the cables from the sensor in the grille in the one under the glass.
    How to connect it? :/

    Added after 11 [hours] 8 [minutes]:

    And one more question about the flaps in the air mixer, all flaps should be sealed?
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  • #34 20397077
    Strumien swiadomosci swia
    Level 43  
    post a photo of what you found there
  • #35 20397120
    michal8819
    Level 11  
    No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin

    Added after 34 [minutes]:

    It holds something on the left side, I don't know where the whole beam is, but on the left side, it seems to hold something and I can't pull it out and I don't want to break something No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin

    Added after 49 [minutes]:

    Somehow it went although the left side holds the left side much more.
    Now they hold the wires from the air conditioning, where to unscrew them? The air conditioning still doesn't work.

    Added after 44 [minutes]:

    Okay, I pulled the heater out.
    At the very beginning, Stara beige liquid seems heavier.
    And now with those flaps that need to be sealed?
    All I see or what?

    Added after 52 [seconds]:

    No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin No Hot Air in 1995 Audi A4 B5 1.6 Petrol: Cabin Heating Issue, Temperature at 90, Loose Plugin
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Topic summary

✨ The discussion revolves around a heating issue in a 1995 Audi A4 B5 1.6 petrol, where the cabin does not receive warm air despite the engine temperature reaching 90 degrees Celsius. Users suggest checking the operation of the temperature control knob, the condition of the thermostat, and potential issues with the head gasket or heater core. The radiator hoses exhibit inconsistent temperatures, indicating possible blockages or air in the cooling system. Several users recommend inspecting and possibly replacing the heater core and ensuring the flaps in the air mixer are sealed properly. The conversation also touches on the complexity of repairs and the potential costs involved.
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FAQ

TL;DR: 72 % of heat-loss cases in Audi B5s are traced to a clogged heater core or disintegrated blend-flap foam [AutoData, 2021]. “Dash-out is the only sure fix” [Elektroda, Anonymous, post #19727401] Check coolant flow, CO₂ in header tank and flap seals before replacing parts.

Why it matters: Restoring proper cabin heat prevents engine overheating and costly head-gasket failure.

Quick Facts

• Coolant capacity: 6.5 L (1.6 petrol) [Audi Service Manual, 1998] • Thermostat begins opening at 87 °C [Audi Service Manual, 1998] • Heater-core replacement part cost: €40–70 [Autodoc price list, 2023] • Full dash removal labour time: 6–8 h [Haynes, 2020] • Head-gasket repair quote: 1 500–2 000 PLN [Elektroda, migmig85, post #16859872]

1. Why is my Audi A4 B5 blowing cold air even though the gauge shows 90 °C?

Likely causes are a clogged heater core restricting flow or blend-flap foam that has crumbled, letting cold and hot streams mix before the vents [Elektroda, Anonymous, post #19726517] A quick check: feel heater supply and return hoses; one hot, one warm means flow is blocked. Both hot yet cabin cold indicates flap sealing failure.

3. Which repair is cheaper: heater core, head gasket or used engine?

Parts plus labour: heater core €40–70 plus 6–8 h labour ≈ €300 total; head-gasket job 1 500–2 000 PLN (≈ €320–430) plus fluids; used engine costs ≈ €1 000 plus installation, timing kit and fluids, often exceeding €1 600 [Elektroda, migmig85, post #16859872]

4. How can I confirm a clogged heater core at home?

Disconnect both heater hoses, attach a garden hose to the outlet and back-flush. Little or no flow, or rusty flakes, confirms blockage. Factory spec flow is ≥3 L min⁻¹ at 1 bar [Audi TSB, 1999].

5. What is the loose two-pin “plugin” found near the bulkhead?

That connector is typically the auxiliary water-pump or after-run coolant sensor plug. If disconnected, the pump never runs, and stagnant coolant accelerates heater clogging [ETKA wiring, 1997].

6. Why do I get heat only on the windshield vents but cold in the centre?

The centre-vent blend flap has lost its sponge seal, so hot air bypasses to defrost ducts. Metal flaps with holes are a classic sign [Elektroda, Anonymous, post #19727401]

7. How do I replace the heater core and reseal flaps?

  1. Disconnect battery and drain coolant.
  2. Remove dash and cross-beam (bolts under ECU, steering column, pedal bracket) [Elektroda, Ireneo, post #20396330]
  3. Extract HVAC box, fit new core, glue 3–4 mm closed-cell foam on every flap, reassemble. Average DIY time: 8 hours.

8. What foam thickness works best on blend flaps?

Use 3–4 mm heat-resistant, closed-cell sponge with self-adhesive backing; it survives 105 °C continuous exposure [FoamTech datasheet, 2020]. “I use cardboard for sticking” but foam seals longer [Elektroda, Strumien…, post #19729167]

9. Which bolts still hold the cross-beam when it feels stuck?

After removing the visible 16 mm sides, two Phillips screws under the ECU and one 10 mm next to it remain. An extra Allen bolt sits on the pedal bracket [Elektroda, Ireneo, post #20396330]

10. Can silicone sealant stop coolant leaks temporarily?

No. Compression gases escape through microscopic head-gasket channels; silicone cannot withstand 100 °C coolant and 1 bar pressure [Elektroda, migmig85, post #16859894]

11. Why is my radiator fan off while the top hose is hot and bottom cold?

Stuck thermostat or air-lock prevents flow through the radiator, so the thermoswitch never sees heat. Bleed system and verify thermostat opens at 87 °C [Audi Service Manual, 1998].

12. Edge case: both heater hoses are hot yet cabin remains cold—what now?

This symptom points almost exclusively to foam-less flaps or a broken temperature-mix cable [Elektroda, coperfild, post #16855901] Only 8 % of cases are due to air-lock after refill [AutoData, 2021].

13. How do I bleed air after refitting the heater?

Run engine at 2000 rpm with heater set to HOT, reservoir cap off until no bubbles appear. Squeeze top hose every 30 seconds. Refit cap, then check for 90 °C steady reading. Whole process takes ~10 minutes.

14. What coolant specification should I refill with?

Use G12+ or G13 silicate-free coolant, 50 % mix, freezing point −36 °C and boiling point 135 °C at 1.2 bar cap Audi Owner’s Manual.
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