gbmarc

I decided, based on the blown fuse and the cold hoses from valves to core, that it was most likely the valve. So on Saturday I pulled out the valve. I disagree with the other poster. It is a nasty job to remove, especially considering how exposed it appears to be. On the passenger side it's very hard to get the hoses disconnected and later on, reconnected. There's simply no room to get fingers and tools in there. I figured it was a lot of work to either remove the master cylinder (bleed the brakes etc etc) or even get at the brake booster to push it aside. (Audi is definitely one of the worst when it comes to total disregard for later maintenance.) So . . . I simply cut the side of the air box and it worked out great. I left a part of the plastic attached so the cut section could just be bent up to allow the valve extraction space. This way, the cut section was still correctly positioned when I came to JB weld the cut back together. When pulling the valve, the hoses from the passenger side are just dragged thru underneath the airbox.
While I had everything disconnected, I ran the garden hose into each core. They were both perfectly clear and water went straight thru.
You might want to clear the drain hole underneath the heater box while you have everything out. It's still not perfectly accessible but much better. I manged to drag some nasty gunge out of it.
Of course, once I had the new(used) valve ready to go in, I noticed something strange about the old one - someone had drilled two holes in the top of the solenoid towers and put a self-tapping screw in each. I haven't opened them up yet to see why, but I suspect it was to force the valves open or closed.
Anyway, after sending water thru the rest of the system and draining/refilling the coolant, I reassembled and "bingo"! nice and warm air blowing into the cabin.
This week I'll dismantle the old valve and see what was wrong. In fact, maybe I'll 'recondition them. The dealer wants $875, so I'll offer mine for only $825 with extra special performance valve screws!

nyrobbie77

glad to hear you got it sorted out. it really isn't that difficult to change it out the "correct" way. I only say "correct" as in the way Audi recommends. We all know there are other ways of doing things, different tricks to skin a cat so to speak.

The following is just to add some information if someone else want to attempt replacing this unit:

I don't recall if I removed just the master cylinder or the booster along with it, but it was only a couple of bolts, not difficult to get to, and unhooking the clip on the push rod at the brake pedal. You only have to remove the knee bolster and a couple pieces of interior trim to do this.

for the passenger side hoses, I was able to get a screw driver in the small space to undo the clamps, adjustable pliers to break the hose loose then pull out from the driver side. to re-install those hoses they slid on fairly easily pushing from the driver side. Despite the hoses being fairly long, they were stiff enough to slide back onto the passenger side heater core connections.

of course once everything is back in place you will have to bleed the brakes. I had just bought the car and wanted to do this anyway as I didn't know how long ago it had been done.

Overall its not a terrible job, but not as easy as say a brake job either.

I replaced my valve about 3 years go with a used unit. Recently I noticed the pump was running whenever the HVAC is on, so I simply unplugged the power connector to it. I had read that some suspect once it runs all the time it is on the verge of crapping out. Not wanting it to die with the valves closed I just unplugged it. I don't ever use the "rest" function, so it is not a big deal to me to not have it functioning.

gbmarc

Just one more update to the story:
I began dismantling the old heater valve unit last night. I found that the pump was dead - no life at all, but the valves looked clear and mechanically, by hand they seemed to work fine. (I'll wire them up to the car on the weekend to see if they operate electrically). But anyway, here's the interesting part - it looks like the previous owner had drilled holes in the top of the black cylinders and inserted self tapping screws to jam the valves closed. In other words he was getting heating all the time and couldn't switch it off, so he then used this brute force method to close off the water flow. So here's my conjecture: When the pump was failing, the 15A fuse blew. As this fuse also controls the valves, the valves were inoperable and of course stuck in the default open (heat on) position. He then screwed them down to stop the heat flow!! I find that really weird. Someone who knew enough to force the valves shut, but didn't know enough to check a simple fuse! So now I'm thinking I had working valves all along and only a dead pump. The valves just couldn't operate 'cause they were screwed down.

Redd

Or, the clever fellow added the screws to force the valves closed. Electrically operated valves?? Which in turn caused them to pull too much current as they tried to open again and which would then blow the fuse?

gbmarc

Yes, not the brightest fix. I took the water pump apart. It was all rusty and gunked up inside. The rotor was frozen but I could turn it after a few squirts of WD-40.
It's hard to see how the water got in there because the seal looked tight, but basically water/coolant got into the motor and destroyed it. The rest of pump, the impeller and the heater valves all look in excellent condition. Back on the car, my used replacement pump is already making a rather loud whirring, so I suspect it's only a matter of time before that one goes out too.