05 Prius-No heat on drivers side

welcome! agree it's likely the vent damper servo. 4k sounds a bit high, try an in depend mech or another dealer. i would have asked for my money back.

 

You'd definitely want it to be the mix servo because that's dead easy to get to under the driver's side of the dash, a few small screws and it's out. But I am skeptical that you'll have that luck, because your heater does not have separate R and L air dampers. Check the diagrams on pages BE-92, BE-93, BE-96 of the New Car Features Manual for model year 2004 (yes, 2004, because the main NCFM is published for the first model year of a generation).

You will see on page BE-92 that the heater core is a straight-flow design and it's fed from the passenger side. I could believe (though I kind of hate to say it) that a gunked-up heater core could produce the symptoms you're seeing. You might try a vigorous coolant backflush before you start looking at disassembly/replacement.

If you end up having to get in there and don't want to spend as much money, the job is a prime candidate for DIY because there isn't anything rocket-sciencey about it, it's just long tedious labor to disassemble most of the dash that's in the way, do your repair, and put it all back together. The labor hours are what you'd be paying the dealer for.

If you go to download the New Car Features Manual, go ahead and pull down the main service manual volumes too, and look over the steps for dash disassembly and getting to the heater core. If it looks like something you could get the hang of, welp, you've just spent $15 on manuals and saved a few thou on dealer labor. But do follow the steps carefully, and don't get any of those fasteners mixed up!

Be sure to check over the procedure carefully in advance to find out if you need to evacuate and recharge the A/C to get access to the heater core. There's no inherent reason you'd have to, but sometimes it's necessary just because of what's physically in the way of what. If that's involved, you should probably just find a local A/C shop to do your evac/reclaim before you start, and recharge when you're done.

-Chap

 

I will add to Bisco's comment, if you need to see a a/c shop, make sure that the shop is familiar with and works on prius systems. The a/c uses a non-conductive oil that is different than normal pag oil. His equipment needs to be contaminant free or you could see a compressor failure in your future.

 

Obviously the dealer didn't want to mess around with it. I give estimates like that when I don't really want a job. I'm curious how the "wrong coolant" got in there and how long ago. You paid for a coolant change and a little extra time to look at the A/C system in the cab.

Since it sounds like cold air at least is moving to the right places at the right velocities, I would suspect a problem with the heat source before a damper.

I wonder if the dealer checked the A/C coolant pump, an electric booster pump to circulate coolant in the heater core especially when the engine is off. There's a TSB somewhere for that, showing how to troubleshoot the system. The pump is controlled by one of the integration relays, so it's more complicated than usual.

I hope not, but I wonder if the wrong coolant did some corrosion damage, and some debris lodged in the heater core. Fixing that would probably mean a new heater core. And If that's a possibility, I'd be concerned about the radiator as well.