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Intermittent Blower Fan

Bronco

NAXJA Forum User
Location
Swansboro, CA
My AC blower fan is cutting out on me. At first I figured and electric short but it mostly dose it as I’m cruising a freeway speeds, and I can always get it to come back on if I let off the throttle a bit. It seems like its vacuum related somehow but wouldn’t vacuum be higher at higher throttle? It dose it no mater if I’m in AC, vent or heat. Should I be looking for a vac leak or could there be another problem. Could it be the switch unit that controls AC? Anyone ever had this?
 
When the fan cuts out, check to see if it really didn't cut out but instead is just blowing out the defrost vents, if so it is probably a vacuum leak. The switch that controls where the air goes is vacuum controlled and with no vacuum it blows out the defrost vents. Mine did this same thing and I found the vacuum leak and it took care of it. My leak was under the coolant bottle but I hear under the battery is a common place for leaky vacuum hoses.
 
seymouj said:
When the fan cuts out, check to see if it really didn't cut out but instead is just blowing out the defrost vents, if so it is probably a vacuum leak. The switch that controls where the air goes is vacuum controlled and with no vacuum it blows out the defrost vents. Mine did this same thing and I found the vacuum leak and it took care of it. My leak was under the coolant bottle but I hear under the battery is a common place for leaky vacuum hoses.
Ok I checked today and you are correct the Defrost is coming on. So dose that tell me that I have a leak in the system or that I have a problem with my control? To find the leak do I start the engine and try to feel for air around the hoses, or is there a better way?
 
I think you have a leak in the system somewhere so when you are on the throttle it can't keep up and there is not enough vacuum and the switch closes. Your switch sounds like it is functioning properly.

I would start at the vacuum reservoir in your front bumper and trace the vacuum lines back from there looking for any cracks, breaks or bad connections. Maybe someone else knows some tricks to finding vacuum leaks?
 
seymouj said:
I think you have a leak in the system somewhere so when you are on the throttle it can't keep up and there is not enough vacuum and the switch closes. Your switch sounds like it is functioning properly.

I would start at the vacuum reservoir in your front bumper and trace the vacuum lines back from there looking for any cracks, breaks or bad connections. Maybe someone else knows some tricks to finding vacuum leaks?
I guess the only thing that still dose not make sense is; why dose is it a problem at high throttle? It seems to me that the more throttle, the more the intake would suck thus the more vacuum you would have? Where is my logic bad? :dunno:
 
Bronco said:
I guess the only thing that still dose not make sense is; why dose is it a problem at high throttle? It seems to me that the more throttle, the more the intake would suck thus the more vacuum you would have? Where is my logic bad? :dunno:

Your logic is bad. First of all, remember that intake manifold vacuum is actually a "negative pressure".

High throttle positions create a MORE OPEN throttle plate. That equates to letting MORE AIR into the intake manifold, creating LESS "negative pressure".

So, the MAXIMUM "negative pressure" is when the throttle plate is closed as tight as it can go. Anything above that is "less negative".

This is what the vacuum reservoir in the bumper is supposed to compensate for.
 
battery acid can also corrode tie vacuum lines where they run under the battery.the slightest leak can cause the ducts to change under load. also ceeck to see if the ceeck valve is faulty. it should let vacuum pass through, but not leak back toward intake when loosing vacuum during acceleration.
 
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