Heater Not Working Properly

Hello

First I need a little more specific on your vehicle to better assist you. Is your model just an A4, or A4 Cabriolet, A4 Quattro Cabriolet, A4 Quattro Sedan, A4 Quattro Wagon, A4 Sedan, A4 Quattro only? Also what is your engine size in liter and the 8th digit of your VIN.

Next, at idle normal operating temperature are the heater hoses going into the firewall both hot or only one?

When the RPM is raised, same question, are the heater hoses going into the firewall both hot or only one?

Has there been anything wrong with your engine temperature at all?

And again, you started having this heater problem "then" you changed the thermostat and you still have the problem?

Do you have Dex-Cool or another brand of antifreeze in your vehicle?

This guide will help us

https://www.2carpros.com/articles/car-heater-not-working

Please answer/do the above and get back with me and let's see if we can get you some steady heat.

Hello - LeahB

Wow, thanks for the outstanding update/information. We don't always get the info we ask for so detailed.

Okay, just a few things based off of what you have said.

First, there is a Technical Service Bulletin (TSB) out on a similar thing. I have attached that for your review. It actually states: "Customer concern of no heat or noticeable drop in heat output in passenger compartment from HVAC system when engine at idle" This is due to the plastic plug as shown. I put the TSB at the end of this.

Next - on the pic below there are two hoses between numbers 1, 2, 13. At idle, is the hose between 1 and 13 the one that is hot and 1 and 2 the one that is cool?

I would first check the plug that the TSB talks about. Even try and replace and see what you have.

Next - I would back flush the heater core. If that doesn't work then you may have to replace the core.

I am hoping it is just the plug from the TSB and worst case, a back flush if not the plug.

You don't have a lot of miles - that is about 6,000 a year. . .not much driving.

Looks like you may have some recalls on your vehicle. The dealer may fix these for free. Please contact the dealer service department, give them the VIN number of your car and have them check on these to see if they apply to you. I have attached those at the end.

Last, for Auto Zone etc. . .sometimes your car can throw a code, the light flash and go out. You might consider that when talking to them in the future.

19 07 01

March 26, 2007

2009949/3 Supersedes Technical Service Bulletin Group 19 number 05-03 dated Apr. 8, 2005 due to revision of a part number.

Vehicle Information

Coolant Leak or No Heat in Passenger Compartment From HVAC

Condition

Coolant Leak or No Heat in Passenger Compartment From HVAC System

Technical Background

Customer concern of loss of coolant, but no leak in cooling system can be found.

Customer concern of no heat or noticeable drop in heat output in passenger compartment from HVAC system when engine at idle.

Both concerns may be caused by a coolant leak from plastic plug.

Plug is installed in engine cylinder block near connection for thermostat housing (arrow).

Improved Coolant Plug.

Service

Other than loss of coolant, a leaking plug can cause air to enter into the cooling system and reduce the effectiveness of the passenger compartment heating system.

Cooling system MUST be tested for leaks with engine cold (below 32 °F / 0 °C) (see ElsaWeb Repair Manual, Engine Mechanical, 19 Engine Cooling, " Cooling system, checking for leaks ").

Tip:
The leak from this plug usually occurs only when the engine is cold (below 32 °F / 0 °C).

If cooling system is tested for leaks with engine warm or hot:

Leaks from this plug may not be detected.

Tip:
Coolant leak from this plug can be sometimes misdiagnosed as a leaking coolant thermostat housing. Always carefully inspect suspected areas to detect the actual source of the leak.

Carefully inspect area where plug is located.

If the plug is found to be leaking:

Remove and replace the plug. Required Parts and Tools

Remove sound insulation below engine.

Drain coolant (see ElsaWeb Repair Manual, Engine Mechanical, 19 Engine Cooling, " Cooling system, draining and filling").

Remove upper engine cover.

Unfasten coolant reservoir and move to aside.

Electrical connector of coolant level sensor must be unplugged.

It is not necessary to remove coolant hoses from coolant reservoir.

Remove oil dipstick bracket bolts (2x).

Carefully remove upper dipstick tube (orange plastic)

Ensure that the O-ring on lower steel tube is not lost when tube is removed).

Remove bolt from plastic plug.

Remove plastic plug from engine block .

Install a new plastic plug and secure with bolt to engine block.

Fastener torque = 23 Nm.

Reassemble dipstick tube and coolant reservoir.

Use the VAS 6096/1 to refill and bleed the cooling system (see ElsaWeb Repair Manual, Engine Mechanical, 19 Engine Cooling, "Cooling system, draining and filling" for details and approved coolant antifreeze).

When refilling engine with coolant:

Always ensure that any trapped air is bled out of cooling system (including heater core).

Recheck for leaks on cooling system (see ElsaWeb Repair Manual, Engine Mechanical, 19 Engine Cooling, " Cooling system, checking for leaks").

Reinstall sound insulation below engine.

Reinstall upper engine cover.

Warranty

Required Parts and Tools

Plug - Part No: 06B 103 033 A

Tip:
Part numbers listed in this bulletin are for reference only. Always check with your Parts Dept. for the latest parts information.

Your system is Automatic Temp Control and is somewhat complex. Needs to be hooked up to a scanner to diagnosis system.

Follow the heater hose from the thermostat housing to the firewall and locate the return hose. Is the return hose cold? Is the supply hose warm, hot, or cold? If warm or hot follow it to a valve and feel the opposite side of temp. Your system may not be so simple but it should have a hot hose to the heater. If it is hot both in and out the damper door on a plenum is not opening.

Make sure as well that there is no air in the cooling system.

With the engine running, hot, and the heat on high, feel both heater core hoses. Both should be hot. If only one is hot, try flushing the heater core. If both are hot, check the blend air door for operation.

Slowly move the temperature control back and forth with the engine running and heater on. Watch for actuators and levers moving on the airbox under the dash.

I imagine coolant level is ok. Coolant gauge on dash read normal? Can you hear the blend door moving when switching from hot to cold?

You may end up having to pull the airbox out from under the dash and put in a new heater core. Let us know what happens. We'll be here.