have replaced fan motor a couple of times (not recently) but have weak airflow with the vent, ac, and defrost modes. when i took the fan motor out, i checked for debris and stuff down in there and didn't find anything - pretty clean. but when the blower is on high, it might as well be on low. i'm thinking those vacuum actuator things aren't opening correctly. i don't hear a leak, but probably gonna have to do a vacuum check to see if they hold open? the fan works in all speeds, so resistor doesn't seem to be an issue, maybe the relay? don't know how it ties in to the fan speed, but... any ideas are welcome... don't really want to have to pull the dash apart to replace those things.

 

A fault with the relay or the fusible link would make the fan revert to lo speed or make it stop altogether. Either there's a problem with the lever so it doesn't go all the way to full speed, or there's a problem with the vacuum actuators as you mention. Can you hear any difference in the fan noise when you switch between medium 2 & hi? Try to apply 12V to the orange wire at the fan relay to test the full speed function. The red wire should carry 12V to the relay. Measure the voltage here also to check for excessive voltage drop when the fan runs. Do this test with the speed selector in anything but hi speed position. Car may be off.

 

the individual fan speeds are working as advertised. you can hear/feel the difference. seems to blow stronger in the heat vents than ac/defrost. i tried to pull vacuum inside the engine bay, but can't get a good seal on that fitting for it. doesn't seem to be much vacuum from the engine for that, but enough to select the different modes. i'm just not convinced that it's blowing as much as it should. defrost in the winter is a prime example cuz it hardly comes out of there.

 

with a little more troubleshooting, i was able to hold a vacuum on that line in the engine bay with the air system off. if i select vent/heat/def, i lose the vacuum and cannot get one in any of those positions. so it seems to be with the vacuum system... one of these days i guess i'll take the control head off and check each part of that system individually. doesn't seem to be any other choice(?).

 

let me know what you find. I've been having problems with vacuum and a/c for awhile now.