Hello,

My '87 Ranger interior cabin fan blows really weak. I only got the truck a few months ago and it's been like that the whole time - are these fans just incredibly weak from the factory, or is there something else I should be looking for? It can't even fully keep the windshield de-frosted when it's only 31 degrees, and I can barely feel it blowing when it's set to panel. Any insight welcome.

Joe

 

Could be a few things
First check voltage at the fan motor in engine bay
It has a 2 wire connector, unplug it
Turn key on
Turn fan speed to HIGH on inside panel
Use a Digital Volt meter hooked to both wires of connector
Should see minimum 12.2volts or -12.2volts
(Brown/Orange wire is 12v, Orange/black wire is Ground, usually.............)
Either means fan motor is getting full voltage
Under 10volts means wiring issue

If full voltage is seen, turn key off, you will need to pull out the motor, just 3 or 4 screws
Once its out check that the squirrel cage fan is tight on the shaft of the motor, should be a set screw holding it tight to shaft
Turn key on
Fan still on high
Carefully plug motors connector back in, motor will JERK from torque
Should be turning very very fast
If possible have someone turn fan to low, med and high as you watch motors speed change
If its not changing speeds then unplug it again
Use voltage meter again on the 2 wires
Low should of course have lower voltage, med slightly higher, and HIGH is full battery voltage, if you see that then Block resistors are OK, replace blower motor, its bad

If Fan seems to be working OK, reach your hand into the blower housing and toward drivers side, thats where the hole in the firewall is where air from the fan goes thru heater core and out to vents, check it for debris
If you have AC there will be an Evaporator there check if for debris

If you reach in and up thats where the Fresh air comes in for the fan, check it for debris

Wiring issues
Fan motor gets 12volts with key on, always, from a fuse in cab fuse box, usually 30amp
The fans Ground wire is how speed control works
In high the fan motor gets a direct ground
In OFF no ground
There is a Resistor Block in engine bay on the fan motors housing, it has 3 resistors inside
In Low the ground has to pass thru all 3 resistors
In Med it passes thru 2 resistors
In med. high it passes thru 1 resistor

High by passes resistor block, direct ground, so if you only had High speed then it would be a resistor block issue, so not your issue