Ok so I have this weird problem where the fan stops blowing air. It happens randomly while driving. At first I thought my blower motor was going bad so I replaced it with one from the Junkyard.

When it happens, I go through all the settings in the climate control and nothing changes. It'll cut back on after 5 minutes or so.

Could this be the resistor going bad?

 

What Year Ranger?

There is no "vent door" that can cut off all air flow, they can only direct it, default direction is the Defrost vent, this happens if you lose Vacuum in the cab

Resistor block is only used for lower speeds, HIGH is a direct Ground for the blower motor, so by-passes the resistor block

This depends on year but here is an example
The blower motor gets 12volts with Key On from fan relay in the engine bay fuse box, the switch in the cab Grounds Resistor block according to selection, in HIGH the switch grounds the motor directly

 

02 3.0 I don't remember if the defrost vents get airflow. I'll have to double-check.

 

A common issue is for air flow to switch to Defrost when accelerating(low vacuum) and then back to Panel when cruising again(higher vacuum), this would point to a vacuum hose leak in the engine bay or a cracked(leaking) vacuum reservoir

2002 will have Blower Motor Relay in engine fuse box, it is activated by the Vent Selector switch in the cab, when this switch is in any position except OFF, the relay will be closed and sending 12volts to the Blower motor, from fuse #16 40amp

The Fan speed switch is the Ground for the motor as described above, low - med high goes thru Resistor Block, High does not, its a direct ground to blower by-passing the resistor block

This is why people often have no lower speeds but High works, that would be a resistor block problem

 

Ok Ron, it happened again briefly and I think air was coming out the defrost vent only

 

Passenger side engine bay
At the firewall you will see TWO hard plastic vacuum hoses coming out
Grey one goes to Heater hose by-pass valve, only used for MAX AC

Black one is the one you want to follow, make sure there are no cracks/leaks, easy to fix with rubber type vacuum hose, as a sleeve

Follow it to the Vacuum Reservoir, its a black plastic Ball, low down under rad support at the front, often have to get under the front bumper to see it
It has TWO black vacuum line lines
The one you just followed, and one that runs up to the intake manifold, you now need to follow that one to check from problems

 

Ok Ron, it passed the visual inspection. Would smoke testing it be the next step? I have a vacuum gauge too if that helps.

 

If you can find the line that connects to the intake manifold you can suck on that line and it should HOLD a vacuum.

Vacuum doesn't get "used up", should just hold "forever" but smaller leaks will happen which won't effect anything, yours is a larger leak

If intake line doesn't hold vacuum then you will need to disconnect the line from the reservoir, the one that goes to the fire wall, and test if it can hold a vacuum, if it can then the Cab system is OK, most likely problem is a crack in the vacuum reservoir which is not all that uncommon
Ford used standard size reservoirs so pretty much any Ford car or truck in a wrecking yard will have one that's the same as yours

 

Ok finally got around to testing the vacuum hoses.
The one that goes to the firewall starts leaking vacuum slowly. I followed the black hose to under the glovebox and disconnected it to test it individually to see if it holds vacuum, and it did. So did the hose that runs to the climate control **** and the other end, that connects to the vacuum reservoir.

They each hold vacuum individually, but I still lose vacuum when all connected if you follow me.

Then, i tested the vacuum reservoir at each port and it holds vacuum, too??

The other hose that runs to the intake wasn't holding any vacuum, but when I individually test the hoses, they do? So that rules out any cracks in all the hoses?

 

I did some more testing and the hoses do hold vacuum when I plug the black or white/grey hose(for heater control valve) from the harness to the climate control ****.

HCV hose, white hose plugged at harness



Black hose plugged at harness






Ron, as to testing the hose that runs to the intake, do I unplug it from the black ball and check for vacuum to the intake, or from the red hose and check for vacuum to the black reservoir ball like in the photo.

It doesn't hold anything either way. Only when I disconnect it from the red hose, and plug the hose as mentioned.

 

The black ball should hold vacuum if the firewall hose is connected, that would mean the cab system doesn't have a leak

If it doesn't then unplug the black hose at the black ball and plug that port, test vacuum again, if black ball doesn't hold vacuum then replace it

If black ball does hold vacuum then put vacuum gauge on black hose and see if you can hear where vacuum leak is in the cab system

The vacuum source, intake manifold, line can be "T"ed a few times, doesn't matter as long as there is a Check valve, either built into the black ball or on a direct line to the black ball

You can test if black ball has a check valve built in by blowing into both ports one at a time
If you can blow air into both ports then no built in check valve
If you can't blow air into one of the ports then that port has a check valve built in and would connect to the Intake Manifold

 

Will try that when I get a chance. I did find yesterday that the system holds vacuum when the switch is on the 'OFF' position but starts to lose vacuum when I switch it to MAX AC

 

Check the Grey hose in engine bay connected to the heater hose By-pass valve, only time that is used is in MAX AC

Also the Fresh air vent is closed in the cab in MAX AC, its Vacuum motor is behind glove box

Those are the only differences in MAX AC

 

I had a similar problem where air would be redirected to the defrost vent when using a lot of power, then eventually it just did that at all times. Was the vacuum hose that runs between the accumulator and the coolant overflow tank, rubbed against it and had a hole. I just fixed it with some heat shrink tubing and covered that with duct tape as armor.

 

Finally FIXED my problem!!


Turns out the back of the climate control **** where the hoses hook up to had a broken connector causing a leak somehow. You can see where I tried some silicone on it. It started to hold vacuum but was still slightly losing it at a much slower pace. Replaced it, passed the vacuum test and took a drive on the interstate 70+ mph and didn't switch to defrost

 

Good work

Yes, thats a hard one to find because it doesn't happen that often

Thanks for posting the FIX