Anyone ever replace the air temp control servo?

[pplassm]

All indications are that the air temperature control servo on my 1990 GT-S has failed. The cable to the water control valve does not move. I have disconnected it, and can manually control the water to the heater core, but I cannot get the air flapper to move, so the air coming into the car is a mix of air coming over the heater core, and the evaporator.

Has anyone replaced this part? How bad is it?

I removed all of the accessible plastic panels, and started removing components, but it appears that the only way I am going to reach it is to remove the entire dash panel!

This is assuming that it's on the bottom of the heater box, as I cannot find a description of its location, or a decent photo.

Am I going to have to remove and drain the heater core and evaporator, too?

What a nightmare.

Thanks!

[85HILUX2WD]

I have an 89 Celica GTS so I know we are talking about Gen 4 and Gen 5 here but I had a similar problem that I thought pointed towards my air temp control servo. I have the automatic climate control unit and I stopped getting heat into the cabin. I, like you could not get the servo to actuate the hvac control. The problem ended up being within the climate control unit. I removed it from the dash and had a friend open it up. Turns out after 20+ years of vibration several of the saudering connections had failed. He fixed it and charged me $150 and the unit has worked flawlessly ever since. Just a thought since it sounds like a similar problem. I don't know if you have the cable driven HVAC controls or the electronic ones like mine