I speak 240 so that being said. The cable to the heater valve is bent or has slipped at the securing point,therefore causing it to bottom out early . That will perhaps help. The real problem is leaking moisture . Does the door panels have plastic barriers that are sealed ? The moisture getting in is problem1 Needing the heater to resolve it is problem2. Worn rubber seals also cause this.IF the car has working A.C. that will kill it fast,as it takes the humidity from the air rather than trying to act as a clothes dryer with the vent closed. The last fix comes from my scuba diving training. If you spit into your mask and rub it around it won't fog. Errr--Just dont do it on a date!!!

to repair the seal on the heater , I used the closed cell foam that is used to wrap glass ware for shipping . It comes on a roll and is about 3/16'' thick and it works vary well so far. It's been on over a year now.