Help with vacuum leak
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Cargo Master
Joined: Sep 2015
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Help with vacuum leak
Hey guys, AC is stuck on defrost and I can't find a vacuum leak anywhere. Pump just runs and runs. If I disconnect a vacuum hose and hold my finger over it it pulls a really good suction. I hooked up my smoke machine which usually finds the leak very quickly but I am seeing no smoke come out anywhere. Any ideas of what I can check next?
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Cargo Master
Joined: Sep 2015
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Also the blower motor kept randomly cutting out and eventually died . I put in a new motorcraft blower motor and it is glowing great now but only through defrost. Before the blower motor blew it would blow out of the other vents. It was only after replacing the blower motor that it started blowing only through defrost. I have checked all of the vacuum lines. This truck does not have automatic hubs so no vacuum lines going to the wheels for four-wheel drive
FTE Chapter Leader
Joined: Jan 2005
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From: Henderson, NV
Well, smoke is not going to come out because it is a vacuum. You could try gently pressurising the system with smoke.
Alternatively, you could use an HVAC leak detector to find it.
Alternatively, you could use an HVAC leak detector to find it.
Last edited by FordTruckNoob; Feb 13, 2026 at 08:42 AM.
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Cargo Master
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Yes that is what I have, it's a smoke machine with a built-in compressor specifically for vacuum leaks. It's made by autoline pro. I have used it to find a leak on my other truck and it worked great. I just can't seem to pin this one down. The vacuum pump is only about 3 years old and it is pulling a good vacuum but it is still stuck in defrost. I'm wondering if it may be the dash ****?
FTE Chapter Leader
Joined: Jan 2005
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From: Henderson, NV
Yes that is what I have, it's a smoke machine with a built-in compressor specifically for vacuum leaks. It's made by autoline pro. I have used it to find a leak on my other truck and it worked great. I just can't seem to pin this one down. The vacuum pump is only about 3 years old and it is pulling a good vacuum but it is still stuck in defrost. I'm wondering if it may be the dash ****?
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Cargo Master
Joined: Sep 2015
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I haven't but I will try that. Just thought it was odd that when the blower motor went out the defrost issue started happening
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Cargo Master
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I put a vacuum on both actuators and they worked fine so I hooked up the smoke machine again and finally found the leak. It was a tiny little crack in the vacuum line that comes off of the vacuum reservoir and goes into the cab. It was so small that I couldn't see any smoke but I started noticing oil from the smoke machine building up on the vacuum line. Thanks for your help FTN
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Cargo Master
Joined: Apr 2012
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From: Bottom Of Pikes Peak
you checked all lines under the hood and mainly to the hubs? Majority of the time the issue is under the hood somewhere but can also be in the cab. It's a pretty simple system, so it shouldn't be too hard to figure out; I wouldn't think
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Cargo Master
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Post #7 👍
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From: Oologah, OK
I put a vacuum on both actuators and they worked fine so I hooked up the smoke machine again and finally found the leak. It was a tiny little crack in the vacuum line that comes off of the vacuum reservoir and goes into the cab. It was so small that I couldn't see any smoke but I started noticing oil from the smoke machine building up on the vacuum line. Thanks for your help FTN
I also have a smoke machine, and need to get to work isolating where the leak is.
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Cargo Master
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On both of my trucks I had a tiny crack in the vacuum line going from the reservoir into the cab
FTE Chapter Leader
Joined: Jan 2005
Posts: 13,110
Likes: 4,715
From: Henderson, NV
I put a vacuum on both actuators and they worked fine so I hooked up the smoke machine again and finally found the leak. It was a tiny little crack in the vacuum line that comes off of the vacuum reservoir and goes into the cab. It was so small that I couldn't see any smoke but I started noticing oil from the smoke machine building up on the vacuum line. Thanks for your help FTN
