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

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.

Best HVAC controller troubleshooting video I have found.

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

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%

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.

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.

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.

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

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.

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!

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.

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

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!!

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!

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

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

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.

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

Thanks for demonstrating the diagnostic approach and smoke test !

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

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.

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

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!

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

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.

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)

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

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 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.

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

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

Thanks much for posting these videos!

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.

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

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!

Professional tools and diagnostic methods. Great video!

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

Great video . Thanks. Extremely helpful!

Fantastically clear video, great instruction!

You sir are a teacher, Thank You

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.

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

I learned a lot today from your video! Thanks!

What if you have no air flowing from the front vents at all? I don't notice any airflow on any fan setting, AC, heat, or defrost. Has it still defaulted to defrost? I have replaced the 3 AC fuses under the steering wheel, the blend door actuator relay, the blend door actuator, the blower motor, and the resistor. Still no air flow. 2001 excursion 7.3 2wd. Rear ac blows cold. No air flow at all to the front. I'm going to try this vacuum diagnosis and see what happens. Best video I've ever seen, great teacher.

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 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.

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.

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

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 !!!

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

An excellent no-nonsense walk through. Thank you.

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

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

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

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

This man finds the problem and fixes it, amazing

Great video. Clear and to the point.

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

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

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.

Yes, the absolute best video on this subject . Hope it helps with my problem. Thanks !!!

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.

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

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

this is a gold lesson thanks guys

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 instructional video. I like the vacuum test. thanks.

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!!

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

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

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

This guy is awesome! so much knowledge

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

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.

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

Will definitely be looking into this. Thanks

Excelente, muchas gracias. Muy instructivo.

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 :)

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

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

You are awesome! Thank you so much!

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

Thanks for the video - great information!

what smoke machine is that and what range does the gauge has to have? 30hg?

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

Exactly what I'm dealing with! TY!

another great video. Thank you

Great video!

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?

Old timers would just blow smoke into the line with a cigar/cigarette but your fancy smoke machine is cancer free and prevents vehicle owner complaints of cig smell. 😆

Thank you so very much sir. You fixed the problem

fantastic advice!

Thank you sir. AC fixed. Cost $0.00

Another great video Duane!

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.