2.0 8V bottom end rebuild (by idiots)

[Dieselman]

Cleaning the filters has been on my agenda but it's hot as heck outside and my wife occupies the garage.

Tell your Wife to either move back into the house, or buy a tent.

[Dieselman]

It definitely feels like the cable isn't actually connected as the rotary spins so loosely I didn't even know it was cable operated!

Pull the knob straight off using flat pliers and a rag/bit of rubber, as a cushion. A good grip and quick tug is the best way.
The knobs are held onto the D shaft with a small flat spring clip, which may be missing, or the knob shank be broken which is common, due to being acrylic.
If broken, cut a grove all the way round the circumference and stick it back together using a wire, or strong thread, as reinforcement.

[eyesoreracing]

As your car has rotary heater controls the airflow direction is cable operated. Check the cable is actually connected, the outer sheath is clipped securely and the flaps inside the heater box can move freely.
The A/c issue is most likely the switch is sticky, a strip and clean may sort it.

If the flaps are jammed you have this joy to look forward to. See thread viewtopic.php?f=6&t=6292&hilit=heater+flaps

Oh my god, that link was horrifying!

I've been driving the car daily for a couple of weeks and the A/C works well when vehicle speed is high, but is basically useless when speeds are low. Radiator fans are running when the A/C is on, but are not very strong. But just when I was about to start checking voltage at the fan relay a new problem occured. There was a sudden THUMP noise under the dash, and the vents immediately went from full cold to full hot! The blend door actuator broke or fell off.

We need to figure out how to get down to this blend door and see what happened, but if that means removing the whole dash I might just light a match and run!

[Dieselman]

Your timing is impeccable, it sounds like the blend flaps were stuck so not shutting off the warm air flow, until you left it on full cold while testing and the actuator broke. The cooling fans running slowly is correct for A/c operation.
It would be worth opening the actuator motor unit and ensuring it is synchronised. There are a pair of dots on two gears that must be aligned, otherwise the motor might be over-driving at one end of the rotation and not driving far enough at the other.

I currently am dealing with a blend door actuator failure as part of a heater control issue.
You need to access the blend flap and see if it is seized, if so it's heater box out time, if not you may be able to perform an in situ repair. Fortunately the blend flap actuator is accessible on a Lhd Xm, not easily so on a Rhd, so I have the dash skin and heating ducts out of the car.

My actuator has broken the splined drive and was stuck on hot, so after ensuring the internal flap is free to move, rather than strip the heater box and replace I have used a self tapping screw into the internal heater flap shaft, twisted lock wire and epoxy adhesive to create a new splined drive socket. You need to be careful as the actuator lever is also the bearing for the internal flap to rotate on.