A/C Blows Weak (Leaking Evaporator?) - Ford Bronco Forum
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post #1 of 6 (permalink) Old 08-16-2019, 04:15 PM Thread Starter
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A/C Blows Weak (Leaking Evaporator?)

My A/C has always blown really weak, so much so that my kids sitting in the back seat are uncomfortable on a hot day. I had it checked out recently by a mechanic but the primary complaint was a vacuum leak that caused the flow to shift to floor vents on acceleration. I also asked him to check the refrigerant because I thought maybe low refrigerant was causing the issue. I didn’t ask him to check out the low volume of air specifically. He fixed the vacuum leaks and said the air was 40 degrees and refrigerant was fine.

Now that the vacuum issue has been fixed, the low volume is now a lingering issue. The blower motor seems to be fine and increases/decreases in speed as it should, it just doesn’t blow very hard. I’ve also recently noticed a sweet smell coming from the AC every so often.

My working theory at the moment is a bad evaporator. I understand that could cause the sweet smell but could it also cause low volume A/C? Although, if the evaporator was leaking, you’d think the mechanic would have found low freon.

Any other thoughts on what the problem could be? I’ve seen others complain about low volume air on this forum but haven’t seen anyone post the solution.

Any input is appreciated.

Thanks
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post #2 of 6 (permalink) Old 08-16-2019, 07:29 PM
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The evaporator and heater core are in the same plenum, and I'd suspect that the sweet smell is more likely a weeping heater core. Keep an eye on your coolent level.

The volume of air flow is controlled by the speed of the blower motor. The in dash switch sends ground to the motor through a number of resistors, and on max it doesn't go through any resistors. It is possible that the switch in the dash has built up some resistance itself. I had that happen to me with my Grand Marquis. It is not uncommon for the resistors to burn out and you'll lose some of the lower speeds, but usually the max speed will still work. You may have a weak motor, or poor connections to it.
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post #3 of 6 (permalink) Old 08-16-2019, 07:35 PM
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I’d surmise it’s hard to determine if the evaporator is inefficient until the air volume is fixed.

My heater box was chock full of what I’m guessing was bird’s nest material.

You may also have a blend door stuck, ducting in the dash separated, etc.

My EVTM describes a load test that can be performed on the blower to determine (iirc) it’s pulling appropriate amps.

EDIT: one simple test may be to remove the resistor from the heater box and run the blower on high. See if you can block as much air going into the cab as possible. Compare air flow out the resistor opening with what you feel in the cab. It’s a rough test for sure, but may can narrow down where your volume issue resides.
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1980 Ford Bronco Ranger XLT, 351m, C6. My name is Ferguson.
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post #4 of 6 (permalink) Old 08-18-2019, 10:50 AM
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If the mechanic said its blowing 40 degrees then the A/C system itself is fine. A system low on Freon will never blow 40 degrees.

I don't think you have a blender door issue either if the system is reaching temps that low. The evaporator coil cant get colder than 32 degrees or it freezes up and if air vent temp is 40 then its safe to assume the evaporator itself is very close to freezing. Your main issue appears to be air circulation, due to just a worn out blower motor possibly. If the blower motor has been replaced or new then the next issue would be an obstruction such has a dirty coil or something in between the blower fan and the evaporator. Our broncos don't have cabin air filters so the coils can and will get dirty over time.
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post #5 of 6 (permalink) Old 08-18-2019, 05:22 PM
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Check the blend door and blower resistor if it has one.
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post #6 of 6 (permalink) Old 08-19-2019, 12:17 PM Thread Starter
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Thanks all for the responses. It looks like I can get a new blower motor and resister for $80 on Rock Auto so I’m going to throw a couple parts at it and see if it improves. I’ll look everything over while I’m in there and see if anything obvious jumps out. If I solve it, I’ll post it here.
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