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Discussion Starter #1
I've had an issue with the amount of air coming out of my vents ... when driving with it on high it will get down to blowing almost nothing. When I move the position switch it will switch thru perfectly fine .. I've replaced the blower fan , resistor, replaced the climate control face plate and all the switches behind

Any ideas?

Maybe the vacuum pump ? Or the check valve?
M
 

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My A/C wasn't blowing out the front vents only the defrost vents so I replaced the vacuum pump and that fixed the problem good luck MERRY CHRISTMAS :)
 

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Discussion Starter #3
Still an issue , so far I have replaced the following
Blower fan
Resistor
Vacuum pump
Vacuum Reservoir
Climate control plate and all switches
The entire air chamber plenum
All the vacuum pistons on the chamber
Heater core
A/c compressor

Still while driving after about an hour if my air flow is set to high it will die to almost nothing... I can hear the fan shift speeds as I turn the control.. and it makes a whistle when it does it.. any ideas... I ordered a low mile used vacuum line for HVAC ( Ford discontinued manufacturing) and brand vacuum lines for the 4x4 hubs. I'm lost. It seems to come back on when I'm hitting bumps
 

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It sure does sound like a cracked line, connection, or actuator that is holding while the pump is running but then bleeds off over time.

I wish you luck
 

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Start by finding your vacuum manifold and getting some caps to go on the lines.

Then pull one off at a time and plug it, then see if there is a difference in the air flow. This will eliminate all the lines but the ones for the HVAC system but it will give you a place to start.
 

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WHen it does this do you know if it comes out defrost vents and floor or it really blows out nowhere? You know the evaporator is not freezing up? The evaporator has 100% of the air pass through it. It is in the airstream direct from from blower motor. a bad pressure cycling switch can keep it from cycling compressor off.
 

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Discussion Starter #7
Funny you say that. One day I had drove 2 hours or so. When i stopped i popped the hood and the evaporator was frozen over and often has a decent puddle under it after I park. I'll try and link a picture. But I had the freon level checked and was told it was good . It doesn't blow at the defrost vents when it happens
 

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It will freeze more readily with correct refirgerant level on automotive systems.
The accumulator that the frozen line pictured bends and attaches to has a switch on its side pointed at RH fender. That switch is supposed to open the circuit to compressor so it goes off when pressure reaches 23-25 psi as that is a few degrees below freezing (pressure is proportional to temp when full charge is in system). Slight Overcharge can make it not fall low enough but that would have started immediately after the refrigerant was charged for some reason. The switches do fail. Sometimes the switch contacts fuse and it will not open the circuit. The switch is shown here:

https://www.rockauto.com/en/catalog/ford,2005,f-250+super+duty,6.0l+v8+diesel+turbocharged,1430816,electrical-switch+&+relay,a/c+clutch+switch,4284

Local auto stores will have them too for high $20 range.


That same switch also serves to shut off compressor in cold temps due to the same pressure-temp relationship.
 

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Discussion Starter #9
Conclusion

After disconnecting the ac compressor and running the truck up and down the freeway. Everything worked great for just heat ( except for Small whistle or high pitch wind the blower makes)

I then replaced both sensors on the ac lines , high pressure and low pressure, also replacing their pigtails . Drove it Up and down the freeway this morning and afternoon. everything seems to be working perfect except the high pitch. Which is the next issue..

Hope this all helps
 
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