A/C basics...Using manifold gauges to determine a/c problems in a semi truck | a/c pressure readings 

Looks like you know your stuff. I got a problem with my AC, I pulled vacuum for 1hr and it dropped a few psi (2-3) after 10min. If I press the AC button ON the clutch kicks in after I pulled vacuum... isn't that not supposed to happen? So I charge low side and the pressure shoots up way high 100-120psi and the high side goes to like 50-100psi and system won't take anymore (full) no cold air. Ik its a lot but thanks.

Also the AC clutch stays engaged without any charge

3:14

It's not a good instructional video actually. So if u want to avoid more expensive damage. Don't do what he did! Lol.. (I do this for a job)

Don't use 25 year old refrigerant lol

sell that r12 for a pretty penny or use it in older cars

Thanks!

I have a question. My ac starts off cold, an hour after I drive it gets warm. When I stop to idle it gets cold again. I've replaced both expansion valves and the drier. Can it be the evaporator?

Much appreciated

@@DIYSEMI Your welcome

A REAL HARD LEAK TO FIND IS WHEN YOUR EVAPERATOR IS LEAKING IT WILL HOLD A PRESSURE TEST AFTER A VACUUM HAS BEEN PERFORMED AND WILL LEAK THROUGH YOUR EVAPERATOR DRAIN WHEN YOU RUN THE AC UNIT AFTER 5 MINUTES OR LONGER I DIAGNOSED A CAR WITH THAT PROBLEM HAVE A NICE DAY ASE TECH AND BEHOND

U do have a leak. Yr sytem failed the vacuum test.. it should hold 29 hg indefinitely. Next step would be yo pressurerize it with nitrogen and soapy bubble spray to 'hopefully' find the leak. If that fails. Next step is to recharge it with ac dye added. This dye goes round the system and exits at the leak site. After having it ran dry, darken out the vehicle bay and shine an ultra violet light on all the hose and connections and components. When you see a green dye trace, you found the leak.. this is the most successful leak finding method in the arsenal and every ac specialist should have it on offer. And this is what u need to do to actually solve the problem.. we do this successfully everyday..

@@franshuber910 I certainly want to thank you for responding to my issue. It was by pure luck that while I was checking out the engine for an upcoming trip, I noticed some wetness on the corrigated plastic cover that covers each of the A/C hoses that come from the pump. One was wet about a foot or so from the fitting on the pump. Hmmmm. So, I peeled back the plastic cover and what I found was what looked like a potential repair with crimped fittings and all. It was fairly oily around all that part right there. I had to assume that was where my leak was and no one in the service center where I'd paid to have the system checked out , vacuumed and filled, bothered to look there. After determining that hose was the short one that led to the evaporator, I had a new one made up and installed it. I then vacuumed the system down to 29.5 inches and it held for as long as I wanted it to. I then filled the system with the required 40 ounces. All that was a couple or more months ago and each time I'd got into the coach and fired it up after I'd done that work, the A/C was cold and nice. So, I think I've fixed my problem. It's winter now here in Southern AZ so, I'll check it out when things warm up in the future. Again, thank you for responding here. Very much appreciated.

Mate!.. lol. It's totally incomplete and done wrong! 😂

cool

Thanks for the sub!

Sub to AM PM Mobile Repair for Owner Ops tips and tricks

Yes, they can be equal

Yes it can be expansion valve

@@DIYSEMI Thank you so much sir, I will try that :)

i can only show so much because some parts of it are illegal to do by yourself without a license

possible high pressure, but it could be due to that extreme heat. is it happening when it's not quite that hot out? Gosh dang that's hot. I would melt

@@DIYSEMI So last night when it cooled down a little bit the fan started cycling normally again at idle. It guess its from the heat. Its so dang hot lol.

That is possible. Also while u are in there check your blend door actuator

Some ac systems will make hissing noises when they are low on refrigerant. It's the sound of gasses moving through the pipes rather than a liquid.

Yes, if everything just got fixed i woudnexpect it to be 40-50 degrees from the vents.

I show how to deal it in my blower motor video. At the end

Sounds like you have super high pressure. It's probably happening with heat on because compressor turns when defrosters are on. You probably have a bad obstruction somewhere in the system building back pressure.....I would have it looked at.

low pressure side

@@DIYSEMI I got same truck you have ,is it the side with the blue gauge connected to it?

Possible that the evaporator is freezing up? Does it drop water out under the truck like a/c normally does? Did u look at that discharge temp sensor inside the dash? Just a thought

Yes, sounds like a high pressure situation to me. Could be several causes. Overcharge system, restriction in system...etc

can find them online, or they usually come with a manifold kit.

should be a sticker on the firewall that will tell you

W900 Kenworth

does the a/c cool as it should with no issues? My first thought would be were you careful to add the exact amount of refrigerant to the system? an overcharge can cause this. couple other things, do the pressures equalize when you shut off the truck? are you warming up the truck before testing pressures? temp is important as well as airflow. does the fan bring the pressure down quickly or does it struggle? I would run the truck for a good while..see if you get different readings with everything up to temp.

@@DIYSEMI yes the pressures does equalize when I shut the truck down and also with the fan kicks on it does pull the Pressure down quickly, I had to leave out today so it’s doing great with the AC set on outside air vent , on my little thermometer I have stuck in the vent is showing 40° fan is on two speed, so it’s doing great I won’t be able to check with the gauges until I get back home. Thanks for your response and your video looking for more stay safe.👍🇺🇸

The compressor broke down, so I replace it and the dryer too , and after that my engine fan it’s kicking in constantly after stops running kicks in right away, and the ac isn’t cold no more

Can I ask what kind of problems are you having? Does the a/c not work? does the compressor run as it should? or when the pressure drops and does not come back up, is the compressor not kicking in? It can be multiple thing causing problems like this

Good explanation didnt no how to use my set the right way

4 oz is way more than enuf. Did u look at the evaporator inside your dash for leaks? And in the bunk?

@@DIYSEMI I looked under the bunk at that evaporator there but I have not looked closely at the evaporator in the front.

Depends on the truck. There should be a sticker on your firewall that says how much

Put a can in with some dye to find your leak

@@DIYSEMI thanks for the information

The bigger fitting is high pressure. Smaller fitting is low. You can only hook up one way.

@@DIYSEMI right on man. Thanks, I guess when I replaced my high pressure switch I put it on the lower line

Yeah. Even a small one....just takes longer

@@DIYSEMI Ok, thank you. Going to attempt this tomorrow. How much or how many cans of refrigerant?

Should be a sticker on your firewall saying how many ounces

did you check to see if you have power to the compressor? probe the plug. look for a 12v reference

@@DIYSEMI yes and there’s no power so I checked the compressor clutch jumped it and it works and blows cold I’m thinking it the high or low pressure sensors

@@TheBreedxxx very well could be

Any auto parts store..,harbor freight too

sounds like a restriction somewhere

Because people on the internet can't behave themselves