911SC A/C Evaporator Fan Problem
 

I have an '82 911SC with a Griffith's A/C system with 3rd condenser, rotary compressor, upgraded front condenser and upgraded evaporator core. My car also has a 964 dash with the bigger vents and additional vents from Griffith's. The system has worked great and really cools well!
However, today, I started the car, turned on the A/C and the vents weren't blowing! I don't know if it is related, but recently I had occasionally heard a squeal from what I assumed was the evaporator blower motor (like an idiot, that's about the only thing I didn't replace with the Griffith's upgrade - supposedly the motor had been replaced just a few years ago!). When this happened, I shut down the car and in a few minutes, cranked it again and tried the A/C and still no luck. I also noted that the Griffith's 3rd condenser fan was not running in addition to the evaporator blower fan not running.
The original #20 position fuse had previously been removed and there was a power lead coming from that area with 20A in-line fuse that was blown. I looked in the Bentley manual and it called for a 25A fuse, so I replaced it with a 25A. This caused the condenser fan to run again, but the vents still weren't blowing and the evaporator fan wasn't running. The 25A fuse did not blow. To further add to the confusion, the fresh air blower fan motor is not working now, either. It previously ran without problems!
The A/C fan switch in the car still works in that it turns the condenser fans on-and-off.
I finally opened the smuggler's hatch and located the power wires to the evaporator blower fan. I jumped 12V across the wires and the fan motor tried to run for a second or two and then quit. With subsequent attempts it didn't work at all.
Should I just assume I have a burned-out evaporator fan motor and replace it? If I do, I plan to discuss it with Griffith's and probably upgrade to their fan motor. Are there any other diagnostic checks I need to do first? I can't believe the fresh air fan motor burned out at the same time - will restoring the evaporator motor restore power to the fresh air fan motor???

Check the relay in the smuggler's box?

Well ... this is embarrassing. I solved the fresh air fan problem! It was related to the A/C evaporator fan problem - but not like you think - apparently, I had accidentally dislodged the fuse while checking fuses and relays. Replaced the fuse and it works great!

Now on to the real problem! I double-checked again and apparently the evaporator fan is definitely kaput. 12v applied directly to the terminals usually does nothing - once or twice it "grunted" like it was trying to start but didn't. So, I'm definitely going to upgrade to the Griffith's fan motor which is supposedly 30% stronger, anyway.

I did check the relay and it is OK. I'm getting 12v at the connector to the evaporator fan regardless of the fan speed selected. I'm assuming it works like the fresh air blower fan in that you have to have an operative fan motor connected for the resistors to vary the voltage, correct?

Power from the AC Evap Fan Speed switch goes to the resistor circuit located in the black plastic plenum under the RH foot board and then to the evap fan motor.
If you tried powering the evap fan motor directly with another power source and it did not spin you have 2 choices: good used motor or new motor. R&R will be couple hours max., common tools.

Great minds think alike! I was already intending to call you Monday and upgrade to the Kuehl Wirbelsturm Evaporator Fan Motor. I figured that while I was at it, I'd also upgrade to the Evaporator Fan Variable Speed Controller, too! (if it is not a too difficult/lengthy installation) - I like the idea of eliminating those 34 year-old resistors that control the fan! I have a 964 dash with the larger vents and also the left, right, and center Kuehl vents, so I figure I can benefit from the increased airflow the upgraded motor provides?

I'm assuming that I can retain my thermostatic switch, which seems to work fine. Not a deal killer, but I wondered if I can use my OEM knob with the Variable Speed Controler switch to maintain an original look if I look at the new knobs and prefer the originals (I do want to install the LED, however!)?

I noticed in a YouTube video that the evaporator box apparently used to have a foam gasket atop the outside of the box (I can see traces of where my box had one) ... I've never seen one in any other pictures, etc. What was its function and apparently it's not really needed?

Am I OK with leaving the 25A fuse that I mentioned in the first post?

Before you buy another motor, since you are assuming the current stock unit was replaced not long ago, you may want to insure the blower wheel has not slipped down on the shaft is rubbing on the motor's upper bearing support, or that it has risen and rubbing on the upper case halve.

The host, Pelican, I recall sells both items on this site.

It's at least 5+ years old - maybe 10? It likely saw little use the last few years until I upgraded the entire system and began driving the car regularly and using the A/C. Thanks for the tip - I'll go ahead and open the box (it's going to have to be opened in any event!) and check that out!

Just came back from pulling the fan ... I was pleasantly surprised! The clips slid off laterally fairly easily and I had the top off the box and the fan pulled in about 15 minutes!!!
The motor bearings are almost seized - the squirrel cage fan does not turn easily and there are no clearance issues with the blade assembly. I even removed the squirrel cage blade assembly and the motor shaft is still extremely stiff and difficult to turn.