This is my first post and I'd like to thank everyone that contributes to this forum. My 1984 300TD (turbo/auto trans US market) has climate control issues. Every time I track down a problem and fix it, a few months later another one pops up. Now the floor vents won't open. I don't need AC so I am wondering if it is feasible to install an auxiliary battery with an isolator and wire a 12 volt heater to it? I found some by DC Thermal that are as low as 200 watt w/20 amp draw. Can the stock charging system handle one or even two of them? Any advice would be appreciated.

200W wouldn't even make any noticeable difference in the cabin. Literally the same amount of heat as 2 100W light bulbs. Imagine trying to heat your car with that on a cold day. Not happening, even here in the south.

If you don't care about the automatic aspects of your climate control system, just wire the flaps open to the vents you want. Vacuum issues are very common and can be maddeningly frustrating to solve. Some require dash removal, which at that point it's wise just to replace every vacuum component at once.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thx for the input Diseasel300. I got fed up with chasing vac failures and wired the floor vents open like you suggested. It works great for heat only and I appreciate your advice. It was chilly on the coast this eve so I had a chance to test it fully. I thought it would blow outside air if I was running down the highway with the heat off but it doesn't. I think I will delete my auxiliary water pump to simplify things further. I hear what you're saying about 200 watts not being much for 12 volt heat. I should've been more elaborate. The heaters start as low as 200 watt and increase from there so a more powerful heater is available. The reason I was thinking about the aux battery and 12 volt heater has another motivation as well. I am a working musician and sometimes need to sleep in my wagon when traveling around. That means Hwy rest stops, parking lots etc...... The aux battery would be for light, power a laptop, music and some 'white noise' for sleeping. While reclining in the comfortable seat a little 12 volt heater on the floor with a sleeping bag opened up and draped over does warm things up while I'm winding down and going to sleep. I can use some back seat floor space to mount 1 or 2 Optima sealed deep cycle batteries that don't vent out harmful gases. I'm just trying to get an idea if the charging system on my 300TD can handle charging the extra batt(s). I'd be running down the Highway enough to do some charging. Thx again!!

One of those really quiet generators could run a decent sized electric heater in the car. Most today have thermostatic controls. I do not think it would consume too much gas.

And if the night was really cold you could run the block heater on it for some time before trying to start the car in the morning. I had no choice one time but to leave the engine if one of my 240ds running all night.

It provided adequate heat when it was about 15F degrees outside that night. It was not by choice though. The roads became so bad I could not reach a motel. I slept for about seven hours. It was suprising how little fuel it burnt in the process. I really do not like this approach as the chance of engine fumes are there.

To save money many of us have slept in our vehicles over the years. Remember truck stops are the safest probably. One of my son in laws has used bigger motel parking lots.

I just wanted to add to this post. Just on long trips. I doubt any member has actually lived in their cars.

Assuming you have a 70A alternator, your maximum wattage you can pull (assuming the alternator will carry it) is 840W (12v x 70A). That's including any parasitic draws and the amperage required to recharge the battery. If you're idling the engine, you're going to be easily below half that capacity. If you're sleeping in the car, it might be a better choice to invest in some thermal underwear or some chemical heating packs that backpackers use instead.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I appreciate all the input. The electric heater would only run only for a short time while I'm still awake and winding down. I would never leave it on while sleeping as I have sleeping bags for any temp range that I'm likely to come across.