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post #1 of 13 Old 06-16-2018, 12:02 PM Thread Starter
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Help chasing an AC problem

I have a 99 F350 7.3 and I cant seem to find my issue. My AC blows out hot air. I have changed the vacuum pump, changed the blend door actuator, checked the clutch air gap, checked freon, and still no cold air. The AC clutch has apparently been apart before I got the truck because there is only one washer in it so I couldn't adjust the air gap, right now its at about .05 instead of .02-.03. It was also full of build up around the shaft.....Could I possible need a new AC clutch? The AC Accumulator is getting cold and sweating so I know its working. The vacuum pump seems to run constant so I have to track a vacuum leak but I didn't think that would have anything to do with cold air.....any help?


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Last edited by Locke6169; 06-16-2018 at 02:16 PM.
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post #2 of 13 Old 06-16-2018, 12:08 PM
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Originally Posted by Locke6169 View Post
I have a 99 F350 7.3 and I cant seem to find my issue. My AC blows out hot air. I have changed the vacuum pump, changed the blend door actuator, checked the clutch air gap, checked freon, and still no cold air. The AC clutch has apparently been apart before I got the truck because there is only one washer in it so I couldn't adjust the air gap, right now its at about .05 instead of .02-.03. It was also full of build up around the shaft.....Could I possible need a new AC clutch? The compressor is getting cold and sweating so I know its working. The vacuum pump seems to run constant so I have to track a vacuum leak but I didn't think that would have anything to do with cold air.....any help?


I can attest for the constant vacuum leak. My front hub air locker fittings and tubes are rotten so my brake light is always on. Anyway my pump must also always be running. But my ac is cold after I did the gap mod which entailed of me dropping all the spacers out of the clutch . Not totally educated in ac systems but maybe something is blocked preventing cold air in? Seems odd. Good luck


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post #3 of 13 Old 06-16-2018, 12:18 PM Thread Starter
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Originally Posted by dhide371 View Post
I can attest for the constant vacuum leak. My front hub air locker fittings and tubes are rotten so my brake light is always on. Anyway my pump must also always be running. But my ac is cold after I did the gap mod which entailed of me dropping all the spacers out of the clutch . Not totally educated in ac systems but maybe something is blocked preventing cold air in? Seems odd. Good luck


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My hubs are manual locking. I pulled the last washer out but it allowed for no gap so I put it back in. Did you still have a gap after pulling them all out?


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-Upgraded Early 99 Single Shot Injectors
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post #4 of 13 Old 06-17-2018, 05:44 PM
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Originally Posted by Locke6169 View Post
I have a 99 F350 7.3 and I cant seem to find my issue. My AC blows out hot air. I have changed the vacuum pump, changed the blend door actuator, checked the clutch air gap, checked freon, and still no cold air. The AC clutch has apparently been apart before I got the truck because there is only one washer in it so I couldn't adjust the air gap, right now its at about .05 instead of .02-.03. It was also full of build up around the shaft.....Could I possible need a new AC clutch? The AC Accumulator is getting cold and sweating so I know its working. The vacuum pump seems to run constant so I have to track a vacuum leak but I didn't think that would have anything to do with cold air.....any help?
There should be a plug to the left of the ac with two wires going into it. Wiggle a bit with the truck on and see if the clutch engages. Mine has this problem and is on my todo list. My understanding is that its the high pressure ac switch but you have to drain the freon, switch the plug, and then recharge it.

Edit: vaccum issues with ac only occur if the 4X4 switch is on. makes it heat defrost, i thought.

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post #5 of 13 Old 06-17-2018, 05:49 PM Thread Starter
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Originally Posted by DarthF250 View Post
There should be a plug to the left of the ac with two wires going into it. Wiggle a bit with the truck on and see if the clutch engages. Mine has this problem and is on my todo list. My understanding is that its the high pressure ac switch but you have to drain the freon, switch the plug, and then recharge it.

Edit: vaccum issues with ac only occur if the 4X4 switch is on. makes it heat defrost, i thought.
The clutch engages like normal with the AC switch in the cab


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1999 F350
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-ARP Head Studs
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post #6 of 13 Old 06-17-2018, 06:10 PM
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Have you cleaned your condenser? Could be caked with dirt and debris.

You checked fuse 24 that handles the door actuator? Should be a 10 amp.
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post #7 of 13 Old 06-18-2018, 06:29 AM
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You very likely have a blend door issue.

Blend door controls airflow from either heater core or evaporator core. Obviously it is electronically actuated, you said you changed the actuator. The door could be physically damaged, or the new actuator could be bad, or no power to the actuator, or debris in the bower compartment.

Take the blend door actuator out, plug it in with it in your hand and turn the hvac controller from hot to cold and back to see if it functions. Next with the actuator out try to move the blend door by hand and check vent temps as you move it.

If your accumulator is sweating and cold to the touch then your compressor, clutch, evaporator, condenser, and the like are working(at least somewhat). One line to the evap will be cold the other warm.

All the air directional actuators are vacuum operated. A vacuum leaks will cause a default to defrost, but not no cold air. Also possible is the heater core shutoff valve, but this won't cause HOT air, just not icy cold air.

Lastly manual hubs generally mean a vacuum leak at the hubs, truck came with auto/manual hubs or auto hubs and they stop functioning so easy fix is swap out for Warn manual hubs. If you're blowing air from the vents and switch to 4x4 and she goes to defrost you have a vacuum leak in the hub/nuckle/lines etc.

A vacuum leak will not cause the brake light to be illuminated.......

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post #8 of 13 Old 06-18-2018, 06:53 PM
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What are you seeing for pressure on the low vs high side of the system ?

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post #9 of 13 Old 06-19-2018, 10:48 AM Thread Starter
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Originally Posted by DarthF250 View Post
Have you cleaned your condenser? Could be caked with dirt and debris.

You checked fuse 24 that handles the door actuator? Should be a 10 amp.
Condenser is clear, but will check the fuse. Thanks

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You very likely have a blend door issue.

Blend door controls airflow from either heater core or evaporator core. Obviously it is electronically actuated, you said you changed the actuator. The door could be physically damaged, or the new actuator could be bad, or no power to the actuator, or debris in the bower compartment.

Take the blend door actuator out, plug it in with it in your hand and turn the hvac controller from hot to cold and back to see if it functions. Next with the actuator out try to move the blend door by hand and check vent temps as you move it.

If your accumulator is sweating and cold to the touch then your compressor, clutch, evaporator, condenser, and the like are working(at least somewhat). One line to the evap will be cold the other warm.

All the air directional actuators are vacuum operated. A vacuum leaks will cause a default to defrost, but not no cold air. Also possible is the heater core shutoff valve, but this won't cause HOT air, just not icy cold air.

Lastly manual hubs generally mean a vacuum leak at the hubs, truck came with auto/manual hubs or auto hubs and they stop functioning so easy fix is swap out for Warn manual hubs. If you're blowing air from the vents and switch to 4x4 and she goes to defrost you have a vacuum leak in the hub/nuckle/lines etc.

A vacuum leak will not cause the brake light to be illuminated.......
Never knew that about the hubs. I just thought I dodged a bullet with manual locking hubs when I got the truck. What would you do with the vacuum line when you switch to manual locking...just plug it? I will check all the other suggestions when I get a chance.

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What are you seeing for pressure on the low vs high side of the system ?
Not sure. I had a buddy check and he just told me I was good


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-Upgraded Early 99 Single Shot Injectors
-ARP Head Studs
-AFE Intake
-RiffRaff Up Pipe Kit

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post #10 of 13 Old 06-19-2018, 12:39 PM
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[QUOTE=Locke6169;16106757]

Never knew that about the hubs. I just thought I dodged a bullet with manual locking hubs when I got the truck. What would you do with the vacuum line when you switch to manual locking...just plug it? I will check all the other suggestions when I get a chance.]
If you have a manual transfer case, then I don't think they have the vacuum issue in the knuckle? ESOF(4x4 inob on the dash) then plug them, fold over and zip tie or whatever.

Again a bad vacuum leak somewhere else in the system will cause a default to defrost. If it defaults to defrost when you put it 4x4 then you have a leak. This will NOT cause hot/warm air from the vents because the blend door is electronic.

It will cause your MAX AC not to function properly.

I had an 03 where the refresh/recirculate door arm was busted. From the passenger floor board reach way up to the firewall and the refresh door is hinged horizontally behind a plastic grid. Then a vacuum actuator and a bomarang looking plastic armature connected to the door. I changed mine without pulling anything apart dash wise, but it is a one eye closed, hold your teeth just right, work by faith no by sight sort of thing.

Hopefully it will cool down by Thanksgiving so you can fiddle around with it.

Or chain a generator down in the bed and put a window ac unit through the rear sliding window.....

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Originally Posted by nighthawk285 View Post
Durapig you win the internets today hahahaha
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