Question about Audi A4

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1998 a4 avant. blows cold air. my mechanic says he back flushed the core. i can hear vents moving and the air can be directed both up and down etc. but no hot air.

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  • Ron A Jan 03, 2011

    I need an audi expert not a generic mechanic for this problem. The core has been back flushed. Is there an internal flap valve that directs air over the core?

  • Ron A Jan 03, 2011

    1998 v6 a4 audi.I think all the plumbing is working (the heater core). Is there another possibility, perhaps a flap valve that controls airflow over the core?

  • Ron A Jan 03, 2011

    1998 v6 a4 audi.I think all the plumbing is working (the heater core). Is there another possibility, perhaps a flap valve that controls airflow over the core?

  • Ron A Jan 04, 2011

    this is a v6 audi with the digital temp selection. does it have a cable like you described? thanks

  • Ron A Jan 05, 2011

    decided to double check the heater core. removed shroud and looked at the hoses. both clamps appeared not to have been moved. started the engine and let it heat up. the drivers side hose became hot. the passenger side stayed cool.. actually couldn't feel coolant in the pass. hose. New thought, may be my mechanic didn't check the hoses or back flush the heater core. what do you think?

  • Ron A Jan 16, 2011

    The problem is fixed! The heater core was back flushed and the coolant was topped up or "bled" using a vaccume system. Now blowing hot air. Everyone was on the right track. Lesson learned. DO NOT LET ANYONE TELL YOU THAT YOU NEED A NEW HEATER CORE UNLESS THE BACK FLUSH AND BLEED THE SYSTEM PROFFESSIONALLY. I've read all kinds of blogs about people who have virually rebuilt the hvac when all was needed was to bleed the system adequitly.

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  • Master
  • 2,926 Answers

Your going to have to get under the dash and inspect the heater doors. The door you hear opening and closing is a center door, there is also a temp door that is not activating. Both doors are controlled by a cable and the doors are in a housing assembly in the dash (big job to remove)
If the mechanic back flushed the heater core, than it is good. Otherwise, it the heater core was clogged, you would not be able to back flush it. I have posted some illustrations to guide your repair.

1998 a4 avant. blows cold - ledsled378_32.gif
Center door lever


ledsled378_33.gif
Temperature door

0900c152800c2e33.jpg

Posted on Jan 04, 2011

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  • GetMeOttaHere Jan 04, 2011




    Assembly unit

  • GetMeOttaHere Jan 04, 2011

    YES, that is what controls the heat cables

  • GetMeOttaHere Jan 05, 2011

    You will need to verify the temp and blend doors are activating. There is no easy solution for this repair.

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  • Audi Master
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Have you tried flushing the heater core? Check and re-check radiator for any partial clogged, also check thermostat.

Flush the heater core really good, then refill coolant and make sure you get all the air out. Drain the coolant, disconnect the 2 hoses on the firewall and flush in both directions with a garden hose. It would be nice to put a spare piece of hose on each connection to make it easier and not make a mess of the engine bay, but whatever you have to do.

I do not believe there is a water valve of any kind for the heater core. This document has some directions on draining and filling the coolant and bleeding the air out: A4-S4_B5/Engine/19-1 Cooling system components.

Hope helsp. Keep us updated.

Posted on Jan 03, 2011

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  • Master
  • 4,044 Answers

There is a control valve under the hood, if it doesn't open no water gets to the heater core on the inside of the vehicle. There should be 2 water lines that connect from the engine back tot eh firewall. They are about 3/4" in diameter and normally on the top one there is a valve that is either vacuum, wire or electrically controlled. If that valve doesn't open you have no heat. Since it is winter and you may want to fix the heat now and worry about fixing that valve later you can remove that and replace it with a piece or straight pipe. If that valve is working correctly the problem maybe your thermostat not opening or your water pump not circulating correctly however in most cases if either of those was the problem the vehicle will be overheating.

Posted on Jan 03, 2011

  • James Young Jan 03, 2011

    YA, all vehicles do. If the heater core isn't getting any hot water it won't heat up. If it doesn't heat up you get no heat in the vehicle. The operation of the heating system in a vehicle is not vehicle specific, they all work on the same concept. When you back flush a Heater core you take that valve out of the equation unless your mechanic took a short cut in which case the valve was damaged. Hence the solution provided. Back flushing the system does not insure the heater control valve under the hood is working. If I'm wrong I'm good with that, I gave you a solution that was easily verified. Start and warm the vehicle up, manually open that valve with someone sitting in the vehicle. If you get heat the valve is faulty, if you don't then it is something else. You hear the flap moving so that isn't the problem. You have air coming out so the fan isn't the problem. That only leaves that control valve, low radiator fluid, faulty water pump itself. The control valve is the cheapest and easiest part to check. If that is good, look at the other two areas I mentioned, since a sign the water pump is failing is lose of interior heat that would be your next place to look. Good Luck

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