w123 HVAC blower erratic speed problem

[turbozeke418]

I have a 1980 300TD and the HVAC does not work. I have been using the defogger setting to heat the car for the past couple years since that has its own separate electrical switch. Over the past few months the blower hasn't been operating properly. It speeds up slows down back and forth and is never constant. If I tap on the bottom of the box that contains the fan it will make it run faster. Within a few seconds it will again fluctuate drastically. If I hit the bottom of the fan box, again it will speed up and then fluctuate. Does this sound like a harness issue, or a fan itself issue. I didn't want to buy a replacement fan if there is something else to trouble shoot first?

[toomany MBZ]

You have the dreaded servo HVAC system, I believe.

On later units, cold solder/s in the push button unit itself causes this condition.

If the fan works sometimes on high without blowing a fuse, I would think it is okay.

The possible problem is a flakey connection somewhere.

[cooljjay]

you have the evil servo unit as was said....you have a couple issues....

inspect the servo under the hood of the car on the passenger side, confirm it is crack free and not leaking....if its the aluminum one...you a step ahead...

unplug the aux water pump....remove it and test it, if its froze...replace of clean/lube...

replace the amp behind the glove box along with the temp sensor hose...

remove the blower motor....remove the housing and squirrel cage, clean the motor out with brake cleaner and re lube the barrings with 3in1 oil....

report back,...

[turbozeke418]

my HVAC system is completely inoperable. It doesn't work on any setting except the defroster. I've read that's because the defroster doesn't work off the servo its an electric switch that turns the fan motor on hi instantly. I'm guessing its the fan motor so I guess I'll attempt a cleaning like stated. If not I guess I'll buy a used one.

[cooljjay]

Its not just the fan....doing just the fan will not fix the problem...

read this whole thing!!!!

1971 Chrysler Imperial Auto-Temp 2 Service Reference Guide - Session 281

[turbozeke418]

OK...fans fixed. All i had to do was remove it and spray some WD-40 in the brush area and it works perfectly now.

[toomany MBZ]

Glad to hear of a simple fix.

[BWhitmore]

It sounds like you had a brush that was stuck and the WD40 loosened it up. Any other thoughts on this?

[minsk]

my defroster goes on intermittently...no other heater buttons work..im hoping replacing the monovalve helps. where is the blower fan?

[turbozeke418]

inside the car under the glove box above where the passengers legs would be. VERY easy to remove if you have to.