This is the best video I’ve seen on the vac system and how to properly diagnose it from under the hood to the cab ., what a money saver, experience pays , thank you so much for sharing this, well done sir 😊🙏👍💯

This was more helpful than anything else the search turned up. I should have known the older dudes always know what they're doing!

11 years later and this video was still incredibly helpful. Thank you!

Somebody is not paying this man enough money he is an awesome instructor very talented the way he explains the whole procedure where almost anyone can understand very impressive

Finally someone who knows what they are talking about. Thank you sir!

11 years later and this is still being used. Thanks for education! This is a great video!

Absolutely the best explanation I found in regard to vacuum leak and the hvac. Thank you for taking the time to do this.

Thank you, I've been working on cars for years but I never really understood vacuum lines. after fixing the HVAC door on an Expedition because of your video, I feel more confident about the subject

You’re a Genius sir ! You’ve explained my situation perfectly. Now I know what my mechanic missed in his diagnosis. Wish you were my service guy. Thank you so much for your help and your knowledge.

Best HVAC controller troubleshooting video I have found.

Thanks for explaining the vacuum diagram, you certainly are a master in teaching, you saved me from doing unnecessary work. It turned out to be the hose to the vacuum reservoir. Thanks 100%

The only video that followed the line I need to know thanks

Have to say your videos are some of the best I've seen on KZfaq. Your presentation is outstanding. You have saved me a ton of money . I have to say if not a teacher you missed your calling. Thanks again.

Thanks, you clearly know your stuff!!! Fortunately I watched the second half of your video which addressed my issue with a 2003 Expedition. Before anyone loses heart because they don't have a vacuum gauge or smoke machine, take a look at the check valve and the connections to the feed lines, all 3 of mine were perished and had holes. Fortunately I had some spare line, cut 3 pieces and it is back to good health. Major points from the wife as it is her car. I got lucky, but apparently that is the most likely area to go wrong. Good Luck.

Simply amazing explanation. You took a lot of the mystery out of vacuum lines and check valves. Smoke machine really cool. Excellent troubleshooting and repair. Just subbed.

Couldn’t have done without you. Took me directly to the root cause. Deteriorated hose at the check valve. Replaced the hose and back in business. Thank you!

I become addicted to your video, every day i look for any new vidoes from you. One can understand why knowledge and experience is important from your videos. you are a role model to any one about how to diagnose and find probems, you make most difficult problem in to very simple one. Awesome, Great, Great.. i dont have words to appreciate you. You rock.

Sir, you are the very best instructer I've seen on this king of problem. Thank you so much, I might can fix my problem now, you may have saved me a lot of money. What you said made a lot of Sense to me, God Bless You, (Mac)

I love it when videos explain how the system works instead of just showing what you replaced to fix it. My 2003 f150 was not switching off of defrost ever and I found that the hose on the intake side of the check valve had cracked. Replaced it and boom fixed. Thanks again!

Great video! Opened the hood of my 97 F-150 and had an idea what to look for. The line from the reserve tank was broken and when I tried to disconnect lines from the check valve, it fell apart. All 3 ports just snapped off. Got a new check valve at the auto parts store and connected all the hoses and now I can step on the gas and the AC stays on the vents. Thank you so much.

This is one of the best videos I've ever seen on this subject!! Very informative! Thank you SO MUCH for sharing your knowledge and experience with us!!

Thank you for this video, and your other 3 part video on the heater blend door. Fortunately, this job was much easier than the heater blend door was. For other readers, if you have hot/cold problems it is the heater blend door. If you have A/C vents vs. Floor vents vs. Defroster vent problems, then this video applies. The heater blend door is electrically controlled by a servo motor. The A/C vent vs. Floor vents vs. Defroster vents are controlled by a set of vacuum motor servos (driven by engine vacuum). Usually, as shown here, the problem on the vacuum controlled motors is most typically the vacuum feed lines or vacuum resevoir or the vacuum check valve. (Occasionally the problem is the vacuum servo motor, but that is less frequent.) In my case, I bought a $15 vacuum gauge (Harbor Freight Tools), and was fortunate to have a "really" easy to find leak, that I could in fact hear with my ear. Listen for a hissing sound. If your leak is much smaller, or much larger, then you may not get a hissing sound, and then you need a smoke machine. You can make a smoke machine, there are KZfaq video's on how to make a make-shift smoke machine. One version of it uses a small (low power tire filler type air compressor). You can also buy one of those air compressors at Harbor Freight tools for cheap, but the other parts of the make-shift smoke machine you have to make, and it takes a while. I have one I made from a metal "jar" some Harbor Freight Tool air compressor line fittings, a bit of wire mesh I had sitting around, and some charcoal brickets and some cardboard (cardboard makes good smoke), brickets stay hot under low air compression.

Outstanding video. Very helpful, especially the vacuum-check valve and checking for broken vac lines.

Just what I needed to know for my 01 Taurus. Thanks

Thanks for demonstrating the diagnostic approach and smoke test !

Great diagnostic instruction for both intake source line and component lines downstream. Thank you.

You nailed it! That is exactly what I needed to hear. The mechanic could not find the problem. Thanks

You are SO helpful!! A cut vacuum tube is my problem. You are a very good teacher. Thanks for sharing your knowledge!

Fixed my 1997 Chevy Express Conversion. It was a large Vacuum leak (use smoke). You are very good at what you do "SIR", especially at explaining.

Thank you for such a good explanation. Now I can fix my truck!!!

Very good info,,,I never thought ac on cars was vacuum controled,,, I thought it was electronically...thank u so much!!!

Excellent video! I had the same exact problem on a Ford Van about a year ago. It turned out to be the same exact vacuum hose! Maybe a pattern failure? Thanks for posting this and all your videos. Good job, carry on!

Well done... Great teaching style and very clear instructions. Thanks

Awesome video. I have a Ford Windstar that keeps defaulting to the defrost vents. Now I know what to look for! Thanks, you guys rock.

Very helpful to identify the cause and location of the right vac line. My 2003 Taurus had this issue and the vac line was broken, but hanging by a thread to the grommet that attaches to the dash. I was able to position the house back to the grommet, use some black silicone to seal and strengthen that seam and everything worked as expected. This video was the key for me.

This man finds the problem and fixes it, amazing

Thank you for this video. It saved me a lot of trouble and headaches.

First video was.my issue.. replaced reservoir, vacuum hose and replaced some tubing and I was back in business... thanks for this video..

I really appreciate you for uploading you’re videos I hope you well. Very simple and easy fixing with you’re explanation god bless you sir

Thank You SO Much The Fix and Theory is GREAT Method of teaching !!

Finally someone who knows something and how to explain it.!!!!! Thank you

Great video the actually takes the time to explain how the vacuum control system. I have been troubleshooting issues for days with my van, trying to figure out why I cannot direct the heat where I need it. It is single-digit weather and I cannot get my defroster to work.

I love the way you explain things you make it easy to understand thanks

And I think you meant inches (Hg) of vacuum on the second vehicle. Excellent video on the use of a vacuum gauge. A tool all techs should have.

Thank you so much I just spent 3 hrs under the dash getting to my ac door actuator only to find out mine works just fine, the 2nd part of this awesome video was my exact issue! You are a fkn legend! God bless you.

Professional tools and diagnostic methods. Great video!

You sir are a teacher, Thank You

Very helpful, your a good mechanic. I'll try to remember what you taught me,

Great video . Thanks. Extremely helpful!

Really enjoyed watching your video I dont know any mechanics in europe to have a smoke machine , ive heard of them. Now i want one hope they are not too expensive. Great Video Top mechanic !!!

Fantastically clear video, great instruction!

I really want to thank you for your time to not only inform but to also teach by real life examples for those at home. Like the old saying about teaching someone to fish and they can catch fish for a lifetime.

Thank you for making this video I have the same problem with my 2002 Ford F-150

Awesome video and great explanation for diy fix. Thank you 🙏 for taking the time to youtube!!!

This is the same problem I am having with my dodge, thank you for the video.

What a great video ! This has helped me fix my dakota

Awesome video. You helped me fix my problem. Thank you.

Thanks for taking the time to make these videos. I find the information given here to be THE BEST on all of youtube, and I watch a lot of car repair videos. In addition to your vast knowledge I am impressed with your presentation, very clear and easy to follow. I've been working on cars professionally for more than 25 years and learn something new with each video. Keep up the good work, looking forward to the next video!

great instructional video. I like the vacuum test. thanks.

I learned a lot today from your video! Thanks!

This video saved me a lot of time and money I guess the previous owner was doing something with this and put the valve backwards

Thanks much for posting these videos!

Big thanks to you! Fixed my a/c and solved my problem in 3 minutes.

Very good teacher! That’s the way they all should be explained on KZfaq. It would make it so much easier. Thanks. Now I know what to do.

An excellent no-nonsense walk through. Thank you.

Very Helpful Videos that I've seen you make thank you very much

Thank you very much for your help I did more things than I should have do.

Excellent video and done so long ago. Thank you, I will try tomorrow morning!

Excelente, muchas gracias. Muy instructivo.

I've been wondering where that fishing line goes and why I can't get cold air out of the vents. Now to check behind that battery. Two birds, one stone. Thank you, sir!

Great video. Very informative. I think I can fix my AC problem now.

Wow, as someone else said, a no nonsense explanation and Fix it yourself video...A+

I did learn apparently when there is no vacuum on these models the blend door defaults to defroster setting (so it seems that the default for vacuum based blend doors is 0 vacuum for defrost vent routing) ...All the other blend door positions for front , by feet ,...etc are a certain percentage of vacuum

Great video engineer thank you, I hope your health is back to normal. Thank you again. God bless you.

Thanks for helping with my A/C that was not blowing through the a/c vents. The information you gave me was great and you how the system worked and not just replace everything in the A/C unit.

THE BEST LESSON ON HOW TO TEST VACUUM LINES EVER!!!!! thanks' FOR THE EDUCATION!!

Thank you sir, when i heard you mention accelerate up and the air from front vent transfer to windshield defrost, it's same problem i got on my 03 Expedition vacuumleak tubing same spot behind the battery, the AC is Fixed because you're video, is very helpful , thank you again sir!!

this is a gold lesson thanks guys

THANKS!!!!!! HAD THIS PROBLEM ON A 2000 CHEVY IMPALA 3800....LINE WAS MELTED REALLY BAD....WHICH CAUSED A/C CONTROLS TO DEFAULT TO DEFROST MODE, WITH BARELY NO AIR COMING FROM THE VENTS :)

This guy is awesome! so much knowledge

Great video. Clear and to the point.

Thanks for the detailed description and showing how the system works as a whole. Our 2003 Expedition initially started out as you explained where when going uphill it would quit blowing out the dash vents. Eventually it got to where it would only blow out the defrost no matter what position the control knob was in. I only had to watch the video up until you explained which line left the vacuum control valve and went through the firewall. I took a quick look at the line to see that it was cracked nearly through a few inches below the control. I cleaned both ends up the vacuum hose, slipped a short length of shrink tubing over one end, inserted the other end of the broken vacuum hose making sure to turn it so it would be in a position to reconnect to the control valve, then shrunk the tubing to seal the break. I'm not sure how long it will last but my guess is there's only a tiny amount of vacuum there to begin with. If it collapses I'll try again but make sure to double up the heat shrink. Last result would be to buy a coupling or completely replace the vacuum hose. But for now, it was a 3 minute free fix.

Thank you that was the problem and I fixed it , saved me $$$ ....

Very good information Still chasing my vaccum leak

Will definitely be looking into this. Thanks

@Mutleytech Yes vacuum is measured in inches of Mercury, the chemical symbol is Hg

Thank you so very much sir. You fixed the problem

nice explanation on how to uses a smoke tester machine in vehicles that have blend doors operated by vacuum. But for those that are electrically actuated completely using no vacuum or even worse the old cable driven ones then hope they are easily gotten to or the mechanic will have a ridiculously hard time to switch out the blend door / splice into a cable ...etc depends on car

Exactly what I'm dealing with! TY!

Brilliant video. You regularly find the huge gaps in my knowledge foundation. Say, is there a "poor man's smoke machine" that anybody would suggest?

awesome ! great job!! I wish you around my area. I just replace small hose going into the check valve . Was not it . I need to get a vacuum gage and smoker . Add 2 together and time should just go to a garage.

Thanks for the video - great information!

Great video! I was replacing the worn out rubber boots on my check valve today and the hvac hose came out of the firewall....it is only about 9 or 10 inches long from the T at the check valve to the other end that goes into the firewall....my question is what does this other end connect to and how do I get to what it connects to.

You are awesome! Thank you so much!

Thanks Very helpful and detalled explanattion

another great video. Thank you

Thank you for your time than you for your knowledge 👍

very informative video thank you so much !!!!!

Awesome I believe I can fix my truck now...wish I had a smoke machine, Where can you get the repair vacuum hose

I was having issues with my 98 Cherokee and it turned out that the vacuum line was gone from where the hose gets smaller after the T down to a few inches before the firewall. I have some hoses and I wanna see if it’ll help fix the lack of power too since it’s complete open with a 1/8” hole.