A/C stuck on defrost, any ideas? - Dodge Cummins Diesel Forum
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post #1 of 14 (permalink) Old 09-06-2011, 08:23 PM Thread Starter
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A/C stuck on defrost, any ideas?

Just as the subject title says, my A/C is stuck on defrost. The fan speeds work fine and it blows fairly cold but it won't switch back and forth. Ya'll think it's the selector part or something in the dash? Any help anybody could give would be great. Thanks.


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post #2 of 14 (permalink) Old 09-06-2011, 08:24 PM
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Yes. It is a vacuum issue. Try the search and you will come up with more than enough info to fix the issue.
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post #3 of 14 (permalink) Old 09-06-2011, 11:48 PM
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Yeap... Vacuum problem...

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post #4 of 14 (permalink) Old 09-07-2011, 12:20 AM
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There's a hard vacuum line that runs under the hood from the center of the cowl, fire wall next to the engine to the back of the vacuum pump. It can be knocked loose when working on the truck and cause this issue. ask me how I know.......

check to see if your cruise control works, if this line comes loose that will stop working as well.

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post #5 of 14 (permalink) Old 09-07-2011, 02:06 PM Thread Starter
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Quote:
Originally Posted by bwdt View Post
There's a hard vacuum line that runs under the hood from the center of the cowl, fire wall next to the engine to the back of the vacuum pump. It can be knocked loose when working on the truck and cause this issue. ask me how I know.......

check to see if your cruise control works, if this line comes loose that will stop working as well.
Well now that you mention it...It still "works" but now when I set it, the speed will drop a little over 5MPH before it starts to work. I'll have to look into this.


For anyone else intersted.....Air only comes out of defrost vents

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P-pumped South Bend DD#3850 hydros
AFE Brute Force intake/ Air Dog 150-150
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post #6 of 14 (permalink) Old 09-07-2011, 06:46 PM
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Most likely a vacuum line either broken or loose. As stated check to see if your cruise control and 4wd engages. Both of these are run off vacuum as well. Mine was only working on defrost due to a broken hinge on the air box. It is located near the floor in the center of the dash. This is much less likely but a possibility.
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post #7 of 14 (permalink) Old 09-07-2011, 08:43 PM
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Also check the Switch, If you mean the AC/Heat wont work on anything but Defrost, it could possibly be the switch, that would be a "Gang Switch" If your looking at Schematics of the wiring for the switch it will be a Power Side Control circuit.

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post #8 of 14 (permalink) Old 09-08-2011, 09:15 AM
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i had this issue like 4 months ago its a vacuum line problem mine broke at a 90 right near the power assist

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post #9 of 14 (permalink) Old 09-08-2011, 03:48 PM Thread Starter
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Well I don't know how it happened, but at the end of the line where it T's there's a little rubber nipple that caps the end of that plastic line, and that little nipple had rubbed on something and had a hole in it and that's what was causing the issue.

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post #10 of 14 (permalink) Old 12-06-2011, 01:16 AM
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Ttt

I have the same problem. I only get heat out of the defrost.
My 4wd works fine, my cruise works fine.
Any more ideas ? I took it to the shop, and they told me that the job cost's $750.00..... Because they have to remove the dash.
I don't have that kind of money.

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post #11 of 14 (permalink) Old 12-06-2011, 06:45 PM
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yup most everytime that happens its a vaccuum issue very easy fix

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post #12 of 14 (permalink) Old 12-07-2011, 11:30 AM
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Ok thanks,
I will keep looking

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