[wwest]

'88 Carrera.

Recently when the cabin heater blower in the engine compartment stopped working it turned out to be a defective/failed relay inside the heat control module.

At the "foot" of the two levers to allow heating you will find a microswitch that is supposed to enable the powering of the cabin heater blower. I would check that circuit, switch, first.

Also, the rear cabin heater blower must be drawing the rated level of current flow in order for the two footwell blowers to be powered. I have had occasion when a low battery would result in this effect.