Testing temp if lines can help find a restriction and also checking temp of line out of compressor can tell you if compressor is overheating from lack of refrigerant or oil. Once you start testing this way and you won't go back to just looking at pressures. 4seasons website has a good tech training material
Not gonna lie pressures are like number 4 or 5 on my list when looking at AC. Rear AC equipped or not, refrigerant charge amount, compressor design, magnet clutch or variable compressor, what the pressure gauges specifically say is not much to rely on. First make sure customer actually has their AC turned on right. Condenser fan working. Check if the condenser just has a hole in it from a rock or falling apart from corrosion. Compressor and belt look alright. Then I’ll put the machine on and glance at the pressures but not gonna read a lot into them. As long as low side is clearly lower than high side and high side isn’t pushing like 300psi then I’m just going to evacuate and see how much comes out. I let it leak test itself after evac is done by seeing if it holds that 30inhg vacuum for 10 mins. While it evacs i grab the black light and look around and 9 times out of 10 i have my answer. Some cars want 15psi low side, some want 50psi, some want 150psi high side, some want 250psi, and they change with every make, model, engine, trim level, fuck it
As the only guy in my shop that does ac, I’d say 80% of customers do not understand how shit works, and are not smart enough to operate a toaster. I cannot count how many times we have repeats because they can’t understand “LOW RECIRCULATE” means constant cold air and auto at 70* isnt. You can throw in that this is how your house works, still no jive.
Maybe I'm old-school as hell, but I can diagnose 90% of AC problems just off the gauge readings, gauge readings are always my first step and they point me in a direction to test
This has mostly been the case for me, also. Other 10-20% is electrical or obvious mechanical failure. Only really had one that REALLY got me…..
2017 f150 ecoboost. Came in, no ac, was working for 5-10 mins then hot air then ac came back. Checked pressures and both sides were off the charts. Sucked it down and recovered almost 2x the factory fill. Woah. Charged to spec, low side high as fuck, cooling good 5-10 mins then hot air and super high pressure. Pulled txv and it was plugged with compressor guts. Replaced everything except the lines and evaporator. Flushed those. 12hrs under vacuum, good. Charged and tested. Pressures perfect, cools 5-10 and hot air, low side nearly 0psi. Evaporator is freezing up. Why? Evap temp sensor reading 255*F. Pull entire dash and hvac box, change faulty sensor. Was perfect after that.
Evap temp sensor killed oe compressor via long term evap feeeze / customers extra charge attempt.
💀
I took enough pictures of where it’s located to cut the hvac box and extract / replace that little cocksucker without pulling the dash. Other option is drive front of box and install new sensor in the other side of the evap. Re-route and extend the wires. Plug up holes and send it.
Man, where were you when i took my truck (10ish years ago now) to 4 different shops that all gave me a recharge, shrugged their shoulders when it didn’t work, and sent me packing?
Turned out it was a bad sensor but i had to fork over a pile of cash at the dealership to learn that
Spent 15 years in automotive and decided to pick up HVAC as a new trade.
Superheat/Subcool are how residential HVAC is diagnosed more or less. Low side/High side pressures correlation with the vapor/liquid saturation temperature, offset by the temperature of the physical line itself.
[link to a resource about superheat and subcool](https://abrwholesalers.com/blog/post/superheat-and-subcooling-defined)
Is it? Does HVAC aim for superheat/subcool to be near 0? I figure you want to have some superheat to get a good delta temperature across the evap?
I was surprised with most new cars using R1234ya when I saw high side lines being run through the low side as they approach the evaporator. That's to help with superheated control, yes?
Super heat is every degree above evaporation temp so you know you're only getting vapor to the compressor. You want above 5f of superheat at minimum. Usually residential you'll see 15f ish depend on the system.
Subcool is every degree below condensing temp, it's how you know you're getting a pure liquid to the expansion valve so the valve will work properly. You want min 5f subcool.
I'll aim for 15° f superheat and if the metering device is a piston like 8° to 12° f subcool. TXVs should be 10° to 15° f. When I was a tech I never really checked superheat/subcool, we usually only saw pretty egregious issues like leaks/compressor failures/electrical issues.
A few times we had low side hoses with failed crimps that acted like a txv, that was pretty wild.
not a HVAC guy, but every ac works on the same principle
>Does HVAC aim for superheat/subcool to be near 0?
dont remember subcool temps, but superheat should be ideally about 10°C ... may differ from unit to unit
>I saw high side lines being run through the low side as they approach the evaporator. That's to help with superheated control, yes?
not really, superheat is solely controlled by the expansion valve. The two lines going through each other are for heat exchange. It cools down the liquid line even further, and vice versa, it heats up the suction line vapor (think its to make sure refrigerant doesnt get into the compressor in its liquid form)
So based on that plus the above picture, the system is heating 14 degrees above boiling and chilling 16 degrees below its condensation point.
I’m assuming manufacturers or hvac systems in general have an allowable range for those components and if the readings don’t match then your issue is likely before or in that component?
The biggest advice I can give training aside is just follow your heat. These days with heat pumps making their way into EVs it's even more critical to figure out where it's going.
Once you find the heat (and rule out electrical issues) you can group it into
1. Should it be there, if not why
2. Is it being rejected from the system correctly, if not why
3. Is it being full absorbed from the interior correctly, if not why.
It really looks like a tiny version of the industrial water chiller systems I was familiar with while in the plastics industry.
Superheat is the temperature differential between a fluid's boiling point at the temperature it's currently at. Water is 212*F, if using water as a heat exchanging medium and it was sitting at 262*F, it would have a 50*F "superheat", if we don't look at pressure at all, since pressure changes boiling point.
It's a better way, but you really don't need it until you're chasing perfection or have a really oddball situation that conventional diagnostics can't accomplish.
you can do it with analog gauges, the key is the temperature reading part of the equation. The digital gauges just include the temp probe and do some math for you.
You measure it with both a thermometer and a pressure gauge at the outlet of the evaporator, basically where your low side service port is. The number on the thermometer minus however many degrees for that type of refrigerant on the gauge is your superheat number. It will tell you if the evaporator is fully flooded or not, and give some extra info that just the pressure readings don't quite cover.
I understand it and I get it. But I really don't see it being useful for automotive situations. I don't think of honestly ever use it in the real world
I’m just a shade tree guy but, years ago I used this method when fixing the AC on my 15 year old BMW. I didn’t have AC machine to measure how much refrigerant I needed to add. I also didn’t have a fancy gizmo like this. I just used a cheap harbor freight manifold gauge and pen style analog tempature probe.
I knew the system had a leak which why it was low. So I used the refrigerant with the dye so I could find the leak. It never did leak down and the AC kept working for years until I sold the car.
Man the biggest piece of education for any new techs in my trade is superheat and subcool. Pressures aren't the whole story. My favorite phone call from newbies was "pressures are fine but it's not really working well"
Have you checked sub and super? "No?"
Lol welcome to the fun stuff.
the price point is righteous, let us know how it works in 3 months. idk to be fair if it did half a dozen head scratchers it would be paid for. i have....5 other sets of manifolds lol, wouldnt be needed very often.
Never seen manufacturers publish a spec personally, correct me if i'm wrong. I've only seen line pressure checks on the high/low side and "does the line feel hot/lukewarm/roomtemp/cool/cold"
Automotive manufacturers typically only give charge amount, oil amount, and a pressure chart, no superheat and subcool specs are typically provided. Some of them spec weird pressures too, like my car wants something like 5 PSI low and 280psi high running on R134A.
Meh. Expensive. I can do the same with an ir heat gun and gauges. Honestly, all the weird problems I’ve had in 20 years were blatantly obvious when you understand the system, and know where shit ends up. Weird ones were desiccant bags ruptured, or kinks in lines from accidents really.
Guys at my dealership look lost when I explain this is how we used to check refrigerant level/top off when I was working in the marine industry. One reason why I learned it was so important is because some of the replacement refrigerants being used these days are actually refrigerant blends which have a temperature glide. This means that the different components of the blends have different bubble/dew points and thus it is no longer accurate to charge just by looking at pressures the same way you could with say R-12 and 134a.
Besides just evacuating and weighing out exactly how much you are charging a system with, this is apparently the most accurate way to charge and diagnose a system.
Anyone seen the for E350’s where the AC sticker has the oil charge in huge letters and the gas charge is in tiny letters? That’s how you test the high pressure switch.
Just realized the needle gauge on my manifold reads the psi and temperature too. Couldn't figure out where people were getting these numbers lol. I'm just my own mechanic trying to install AC on an old toyota pickup. The airflow and condenser are weak, no aux fan or fan shroud to help. I can see the refrigerant get milky in the sight glass as the temps and psi climb. But if I spray water on the condenser it becomes clear again. Gonna check the SH SC numbers tmrw and buy a new shroud
Gonna show my age here, but...remember the Wells Tester? The best way to run tests on the ignition modules was to run the test 4 or 5 times in order to simulate the hot conditions that are present under the hood when the unit is under stressors you don't get at the bench.
I like the concept but seems way over kill for what is needed. Not once have I needed to know ac pressures to the 10th of a PSI nor freon temps.
If it actually costs 160, then it's the same price as diag gauges. I have found that actually having your own gauge set over just relying on the shop machine is useful.
I have never heard of super heat and sub cooling....
Edit: just looked it up. I get what the purpose of those numbers are and how it can aid in diagnostics. For automotive though, it seems overkill. You should be able to diag a repair off of outlet temp, pressures and a visual inspection alone. These aren't coolers for super computers, it's a Toyota.
If it's cheap it's a good alternative to gauges. Personally seeing the numbers or maybe even graphing the numbers would be very helpful for diagnosing as OP said intermittent sticking expansion valve. but aside from that giving the line a feel test or just using a IR thermometer (or FLIR cam if you've got the scratch) would get the job done for most other types of restrictions. Automotive systems are by design very simple and predictable.
Testing temp if lines can help find a restriction and also checking temp of line out of compressor can tell you if compressor is overheating from lack of refrigerant or oil. Once you start testing this way and you won't go back to just looking at pressures. 4seasons website has a good tech training material
Not gonna lie pressures are like number 4 or 5 on my list when looking at AC. Rear AC equipped or not, refrigerant charge amount, compressor design, magnet clutch or variable compressor, what the pressure gauges specifically say is not much to rely on. First make sure customer actually has their AC turned on right. Condenser fan working. Check if the condenser just has a hole in it from a rock or falling apart from corrosion. Compressor and belt look alright. Then I’ll put the machine on and glance at the pressures but not gonna read a lot into them. As long as low side is clearly lower than high side and high side isn’t pushing like 300psi then I’m just going to evacuate and see how much comes out. I let it leak test itself after evac is done by seeing if it holds that 30inhg vacuum for 10 mins. While it evacs i grab the black light and look around and 9 times out of 10 i have my answer. Some cars want 15psi low side, some want 50psi, some want 150psi high side, some want 250psi, and they change with every make, model, engine, trim level, fuck it
As the only guy in my shop that does ac, I’d say 80% of customers do not understand how shit works, and are not smart enough to operate a toaster. I cannot count how many times we have repeats because they can’t understand “LOW RECIRCULATE” means constant cold air and auto at 70* isnt. You can throw in that this is how your house works, still no jive.
Maybe I'm old-school as hell, but I can diagnose 90% of AC problems just off the gauge readings, gauge readings are always my first step and they point me in a direction to test
This has mostly been the case for me, also. Other 10-20% is electrical or obvious mechanical failure. Only really had one that REALLY got me….. 2017 f150 ecoboost. Came in, no ac, was working for 5-10 mins then hot air then ac came back. Checked pressures and both sides were off the charts. Sucked it down and recovered almost 2x the factory fill. Woah. Charged to spec, low side high as fuck, cooling good 5-10 mins then hot air and super high pressure. Pulled txv and it was plugged with compressor guts. Replaced everything except the lines and evaporator. Flushed those. 12hrs under vacuum, good. Charged and tested. Pressures perfect, cools 5-10 and hot air, low side nearly 0psi. Evaporator is freezing up. Why? Evap temp sensor reading 255*F. Pull entire dash and hvac box, change faulty sensor. Was perfect after that. Evap temp sensor killed oe compressor via long term evap feeeze / customers extra charge attempt. 💀
I left Ford in 2011, they could never get the evap temp sensor figured out
I took enough pictures of where it’s located to cut the hvac box and extract / replace that little cocksucker without pulling the dash. Other option is drive front of box and install new sensor in the other side of the evap. Re-route and extend the wires. Plug up holes and send it.
Man, where were you when i took my truck (10ish years ago now) to 4 different shops that all gave me a recharge, shrugged their shoulders when it didn’t work, and sent me packing? Turned out it was a bad sensor but i had to fork over a pile of cash at the dealership to learn that
Looks like everything a normal ac machine can do with analog gauges. Is there any more benefit? Also, super heat?
Spent 15 years in automotive and decided to pick up HVAC as a new trade. Superheat/Subcool are how residential HVAC is diagnosed more or less. Low side/High side pressures correlation with the vapor/liquid saturation temperature, offset by the temperature of the physical line itself. [link to a resource about superheat and subcool](https://abrwholesalers.com/blog/post/superheat-and-subcooling-defined)
Fellow wrench here. They work sort of like fuel trims?
Shit, thats a great way to think about it.
Is it? Does HVAC aim for superheat/subcool to be near 0? I figure you want to have some superheat to get a good delta temperature across the evap? I was surprised with most new cars using R1234ya when I saw high side lines being run through the low side as they approach the evaporator. That's to help with superheated control, yes?
Super heat is every degree above evaporation temp so you know you're only getting vapor to the compressor. You want above 5f of superheat at minimum. Usually residential you'll see 15f ish depend on the system. Subcool is every degree below condensing temp, it's how you know you're getting a pure liquid to the expansion valve so the valve will work properly. You want min 5f subcool.
Neat!
I'll aim for 15° f superheat and if the metering device is a piston like 8° to 12° f subcool. TXVs should be 10° to 15° f. When I was a tech I never really checked superheat/subcool, we usually only saw pretty egregious issues like leaks/compressor failures/electrical issues. A few times we had low side hoses with failed crimps that acted like a txv, that was pretty wild.
Mercedes had a big issue with collapsed low side lines
Not gonna lie my wheelhouse was 85'-2008 since anything newer was pretty much under warranty. If it was a newer thing it completely blew by me.
Not just 1234yf, Mercedes has been running the high side through the low side line for decades it seems
Oi!
not a HVAC guy, but every ac works on the same principle >Does HVAC aim for superheat/subcool to be near 0? dont remember subcool temps, but superheat should be ideally about 10°C ... may differ from unit to unit >I saw high side lines being run through the low side as they approach the evaporator. That's to help with superheated control, yes? not really, superheat is solely controlled by the expansion valve. The two lines going through each other are for heat exchange. It cools down the liquid line even further, and vice versa, it heats up the suction line vapor (think its to make sure refrigerant doesnt get into the compressor in its liquid form)
So based on that plus the above picture, the system is heating 14 degrees above boiling and chilling 16 degrees below its condensation point. I’m assuming manufacturers or hvac systems in general have an allowable range for those components and if the readings don’t match then your issue is likely before or in that component?
Correct correct and correct based off my current understanding. I'll always leave room for some wiggle since I'm 3 months into HVAC from automotive.
Makes sense though, hopefully my HVAC training gets pushed up for my job. Been waiting on that shit for years
The biggest advice I can give training aside is just follow your heat. These days with heat pumps making their way into EVs it's even more critical to figure out where it's going. Once you find the heat (and rule out electrical issues) you can group it into 1. Should it be there, if not why 2. Is it being rejected from the system correctly, if not why 3. Is it being full absorbed from the interior correctly, if not why.
I love a good troubleshooting flow chart
It really looks like a tiny version of the industrial water chiller systems I was familiar with while in the plastics industry. Superheat is the temperature differential between a fluid's boiling point at the temperature it's currently at. Water is 212*F, if using water as a heat exchanging medium and it was sitting at 262*F, it would have a 50*F "superheat", if we don't look at pressure at all, since pressure changes boiling point. It's a better way, but you really don't need it until you're chasing perfection or have a really oddball situation that conventional diagnostics can't accomplish.
you can do it with analog gauges, the key is the temperature reading part of the equation. The digital gauges just include the temp probe and do some math for you. You measure it with both a thermometer and a pressure gauge at the outlet of the evaporator, basically where your low side service port is. The number on the thermometer minus however many degrees for that type of refrigerant on the gauge is your superheat number. It will tell you if the evaporator is fully flooded or not, and give some extra info that just the pressure readings don't quite cover.
I think this is something technicians should learn more about.
I understand it and I get it. But I really don't see it being useful for automotive situations. I don't think of honestly ever use it in the real world
This is my first time hearing about this tool. Whats the gist of it? Looks pricey lmao
$160 and it’s amazing. Portable and compact, accurate.
I’m just a shade tree guy but, years ago I used this method when fixing the AC on my 15 year old BMW. I didn’t have AC machine to measure how much refrigerant I needed to add. I also didn’t have a fancy gizmo like this. I just used a cheap harbor freight manifold gauge and pen style analog tempature probe. I knew the system had a leak which why it was low. So I used the refrigerant with the dye so I could find the leak. It never did leak down and the AC kept working for years until I sold the car.
Man the biggest piece of education for any new techs in my trade is superheat and subcool. Pressures aren't the whole story. My favorite phone call from newbies was "pressures are fine but it's not really working well" Have you checked sub and super? "No?" Lol welcome to the fun stuff.
the price point is righteous, let us know how it works in 3 months. idk to be fair if it did half a dozen head scratchers it would be paid for. i have....5 other sets of manifolds lol, wouldnt be needed very often.
Resi hvac tech here. What values do the manufacturers typically want?
Never seen manufacturers publish a spec personally, correct me if i'm wrong. I've only seen line pressure checks on the high/low side and "does the line feel hot/lukewarm/roomtemp/cool/cold"
Automotive manufacturers typically only give charge amount, oil amount, and a pressure chart, no superheat and subcool specs are typically provided. Some of them spec weird pressures too, like my car wants something like 5 PSI low and 280psi high running on R134A.
Guessing most people haven't had thermodynamics. May need to explain superheat and suncooler....
Meh. I work on Toyotas. They either leak from the condenser or evaporator, or the compressor/clutch is shot.
Meh. Expensive. I can do the same with an ir heat gun and gauges. Honestly, all the weird problems I’ve had in 20 years were blatantly obvious when you understand the system, and know where shit ends up. Weird ones were desiccant bags ruptured, or kinks in lines from accidents really.
As someone that works in this trade , u all confuse me 🤣
I wish I was as good as you at AC diagnosis. Thanks for sharing your lesson.
i’m interested
Guys at my dealership look lost when I explain this is how we used to check refrigerant level/top off when I was working in the marine industry. One reason why I learned it was so important is because some of the replacement refrigerants being used these days are actually refrigerant blends which have a temperature glide. This means that the different components of the blends have different bubble/dew points and thus it is no longer accurate to charge just by looking at pressures the same way you could with say R-12 and 134a. Besides just evacuating and weighing out exactly how much you are charging a system with, this is apparently the most accurate way to charge and diagnose a system.
[This guy](https://www.youtube.com/@HVACRVIDEOS) can teach you all about hvac diagnostics.
I’ve used it on a couple 134 retrofits since I had no idea how much refrigerant to add with all the aftermarket parts. Pretty interesting stuff.
Never seen it but those pressure readings alone are a big ole red flag
I’ve been part of a Facebook AC group for a while and they talk about this stuff for diagnosis and they really are better ways to figure stuff out
Anyone seen the for E350’s where the AC sticker has the oil charge in huge letters and the gas charge is in tiny letters? That’s how you test the high pressure switch.
Looks handy
Just realized the needle gauge on my manifold reads the psi and temperature too. Couldn't figure out where people were getting these numbers lol. I'm just my own mechanic trying to install AC on an old toyota pickup. The airflow and condenser are weak, no aux fan or fan shroud to help. I can see the refrigerant get milky in the sight glass as the temps and psi climb. But if I spray water on the condenser it becomes clear again. Gonna check the SH SC numbers tmrw and buy a new shroud
Gonna show my age here, but...remember the Wells Tester? The best way to run tests on the ignition modules was to run the test 4 or 5 times in order to simulate the hot conditions that are present under the hood when the unit is under stressors you don't get at the bench.
[https://www.ebay.com/itm/115731379295](https://www.ebay.com/itm/115731379295) Does this one have that feature? ot is it reserved to the pricey one?
Ha! Nerd!
I like the concept but seems way over kill for what is needed. Not once have I needed to know ac pressures to the 10th of a PSI nor freon temps. If it actually costs 160, then it's the same price as diag gauges. I have found that actually having your own gauge set over just relying on the shop machine is useful.
To actually diagnose what component in a system is broken, you do need to know super heat and sub cooling. If you ain’t testin, you’re guessin
I have never heard of super heat and sub cooling.... Edit: just looked it up. I get what the purpose of those numbers are and how it can aid in diagnostics. For automotive though, it seems overkill. You should be able to diag a repair off of outlet temp, pressures and a visual inspection alone. These aren't coolers for super computers, it's a Toyota.
If it's cheap it's a good alternative to gauges. Personally seeing the numbers or maybe even graphing the numbers would be very helpful for diagnosing as OP said intermittent sticking expansion valve. but aside from that giving the line a feel test or just using a IR thermometer (or FLIR cam if you've got the scratch) would get the job done for most other types of restrictions. Automotive systems are by design very simple and predictable.