subcool/ superheat troubleshoot

[canusayinsanity]

I've been in the trade for several years now and I go thru the forums reading comments of guys screaming at others to post their superheat and subcool readings because its the ONLY way to solve the problem, or saying that these readings will tell you exactly what is wrong with an a/c system. Honestly the only thing I use subcool and superheat for is to charge a system. Whats subcool and superheat gonna tell you that your pressure readings won't? Of course now I can see refrigeration but not a/c work. I'd like see to your guys opinions because to me taking the additional time to take these temp readings and still hunting down your problems seems like a waste of time. I personally only take average of 15 minutes to figure out the problems, worst cases with multi issues maybe 30 min. I'm interested in your guys feed back and seeing how subcool and superheat really help you in your efforts of finding the solutions with a/c issues.

" Tis easier to get hands dirty than to keep clean"

[hvacrmedic]

I have to wonder how many systems you've left running with a partial restriction, and how many you've left running with an undercharge or overcharge. Both are common problems, especially the latter. How do you know the TXV is operating correctly without a SH reading?

[heresjohnnyb]

Don't worry. One day you will realize that these are part of a complete system checkout and troubleshoot. Air conditioning is no different than refrigeration. Refrigeration just has more controls and use various refrigerants due to the temp ranges. Lower temp applications typically use a lower sh range than a/c. You should realize that any real refrigeration issue can be found with the help of these readings. It doesn't matter what temp application it is for. Get used to doing this on a regular basis. I know it takes time but it makes you a better tech than the guy before you or the guy who trained you.

[jrmech]

SC and SH tell you a whole lot of what is going on with a system. How do you diagnose refrigerant related issues without them? Get a book called System Diagnostic and Troubleshooting Procedures and start reading.

[timebuilder]

These readings tell you the what and where and how much of the refrigerant in the system.

How much refrigerant is in the condenser? How much is making it into the evaporator? Is either value "enough" or is it "too much?"

You will NEVER know what a system is doing using pressures alone.

[leaker2]

Touchy feely days are gone. I think since txv's came along for better efficient systems its much more important to be exact on measurements all around.

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[bodhisattva]

Superheat and subcooling tells you where the liquid is and where the vapor is. You can tell if you're stacking liquid in the condenser or if you're starving the evap. Pressures alone can't do that. Pressures will vary with the load. It's like Dan Holohan says, "You have BE the refrigerant." Well, he was talking about hydronics so he said, "you can't see the water in the pipes so in order to know what it's doing you have to "be" the water,... it's a zen thing."

[Tommy knocker]

while I can agree that alot of AC problems can be diagnosed and repaired without this data it should not be dissmissed so arrogantly. The only way to know what is actually going on in the system is to gather and analize as much data as possible. I believe you can find and fix a problem with out them but are you analizing the system for problems? I would have to, respectfully, say no you are not. another thing to consider is that on this forum we cannot see or touch the equipment that posters are asking about. Soo in order to paint a picture of the system in our heads we need as much data as possible. SH and SC will tell you alot about a system if you understand what they are and what they mean. You say you rarely use them I reccomend you start. Check them on every system you touch for the next week, after diagnosing without them the way you usually do. Perhaps you will not find additional problems but maybe you will but regardless you will learn alot more about each of those systems I promise..

[Iceman7997]

Yeah and try explaining to the compressor warranty department how these readings do not have any place in air conditioning. Yes as tommy knocker said that they are needed in the field as a means of setting txv valves but also they are needed to figure out flood back/starve issues leading to premature compressor failure. Most importantly the idea that SH/SC is overkill to you might be true as a lot of diagnosing can be accomplished through touch and feel, and simple pressure readings but walking away knowing your SH is doing the customer, your boss, the equipment manufacturer and yourself a favor. Yeah I used to get furious when the boss started requesting it when you had 20 calls lined up that day and you are about to have heat stroke but I tell him my readings even before he calls or before I even get to the service call. Hahaha JK

[kamersoutdoor]

I remember those days of not fully understanding the concept of SH & SC and its place in troubleshooting!!!

sent from my Samsung Galaxy Note

[GAchillrtek]

I have to wonder how many systems you've left running with a partial restriction, and how many you've left running with an undercharge or overcharge. Both are common problems, especially the latter. How do you know the TXV is operating correctly without a SH reading?

I would like to put my gauges on a system after you leave.....It will tell you Low charge,restriction, Restriction with overcharge, overcharge, low outdoor airflow, low indoor airflow and much more if you know how to use the values you are looking at. If you dont check SH or SC your not doing your job. Beer can cold is not acceptable anymore. When i went to school they had gauges with white out over the pressures for those beer can cold guys who were stuck in their pressure readings. I hardly look at pressure, just saturation temps. Only time i look at pressure is when i pressure up for a leak search, head pressure, certian occasions. always SH and Sc. It will make your life alot easier, unless you dont have any pride in your work. It really irritates me when a co worker calls asking for help, I ask what his SH and SC are, and the answer i get is, uhhhh i dont know i didnt check.... Im not knocking you man, obviously you are on here asking that question for a reason, your on the right track. Alot of guys dont even care to know why good techs use SH an SC in their diagnostics.

[jpsmith1cm]

Lemme guess...

You're "Old Skool" and you don't need those measurements.

Probably don't measure airflow, drybulb and wetbulb change across the evaporator, either.


While you CAN make equipment function by using the "touchy-feely" method, measuring pressure and touching lines, it is not the proper and correct way to do it.

If it takes you a lot of extra time to measure SH/SC then maybe you need to evaluate your techniques because it doesn't take a lot of time to do, really.

Once you fully understand what those measurements are telling you, you won't work on a piece of equipment without taking them.

[ryan1088]

Beer can cold and 70 pounds, all day everyday.

Good example for you....40 ton Mcquay a vintage chiller...our guys have put in 8 or so compressors in over the past two years. I get the call for no ac. I get over there and it's in alarm on freezestat. I start to check things out, reset it, put a set of gauges on and let it rip. It starts to pull down, its running like a 80/250. Both compressors are sweating worse than I was. Sounds good based on your method? Lay the thermometer on it and it's running a 35 degree superheat and a 55 degree subcooling. I think I'm onto something here. Try I adjust expansion valve, no dice. Btw, the outdoor wet bulb was around 70. I get so tired of hearing "well it was sweating back good".

[flange]

Guys, please stop pushing the importance of superheat and subcooling. If everyone learns how ot do it right, my guys will be bored, lol. I just had to send a guy 300 miles to help another contractor who also believed superheat/subcooling didnt matter. My guy got paid to drive there, stay all week, eat out every night, and rive home. WHY?????? because the locla guy was screaming at the manufacturer that their equipment was a pos. the reality is that all of the refrigeration circuits were underchanrged, and one of the had a restriction. The local guy had identified that "charge was correct" on his startup sheets, but refused ot send us his readings.

Please, for the sake of my guys, stop trying to get other to do things right!!!

[canusayinsanity]

I will do that.. started a couple weeks ago for a day but been on vacation since then lol This week I'll be putting it to the test. To the guys who assume I'm some second rate tech who just slaps on gauges and walks away, I don't. I have a lot of pride in my work. I been behind a lot of seasoned techs well over my years of experience and have fixed their mistakes time and time again- As well as sub contractors that handle some of our clients when the job is too far to justify driving ( tech expense and fuel costs) Mind you I can see all you guys are great techs no doubts about that. I will take all your guys advice and take sc n sh readings more often.

[canusayinsanity]

I'm interested to hear what you found was wrong, maybe I missed it but what was the problem you found if you can recall. I know I cant recall a lot of service calls myself lol

ryan1088 posting in this thread

[jpsmith1cm]

Guys, please stop pushing the importance of superheat and subcooling. If everyone learns how ot do it right, my guys will be bored, lol. I just had to send a guy 300 miles to help another contractor who also believed superheat/subcooling didnt matter. My guy got paid to drive there, stay all week, eat out every night, and rive home. WHY?????? because the locla guy was screaming at the manufacturer that their equipment was a pos. the reality is that all of the refrigeration circuits were underchanrged, and one of the had a restriction. The local guy had identified that "charge was correct" on his startup sheets, but refused ot send us his readings.

Please, for the sake of my guys, stop trying to get other to do things right!!!

Don't DO stuff like that.

I almost spit my drink all over my screen.

[akelesis]

SC and SH tell you a whole lot of what is going on with a system. How do you diagnose refrigerant related issues without them? Get a book called System Diagnostic and Troubleshooting Procedures and start reading.

ya i bought myself the book its an easy read and there is a lot of important information there. but like everyone says reading something and actually doing it the system will make more sense and you will have less call backs

[ryan1088]

I'm interested to hear what you found was wrong, maybe I missed it but what was the problem you found if you can recall. I know I cant recall a lot of service calls myself lol

ryan1088 posting in this thread

The expansion vavle wasn't feeding enough refrigerant. With that came along poor compressor cooling, oil return, and all that fun stuff that goes along with a starved evaporator. Then they would go boom. The freezestat trips came from the same starved evaporator issues. There's obviously an internal problem with the valve or clogged screen causing the problem.

My point was that everyone that has worked on this prior in the past few years only looked at pressures and this problem eluded them many times. Once you see the whole picture with line temperatures and saturated temperatures, things get so much easier.

[GAchillrtek]

I will do that.. started a couple weeks ago for a day but been on vacation since then lol This week I'll be putting it to the test. To the guys who assume I'm some second rate tech who just slaps on gauges and walks away, I don't. I have a lot of pride in my work. I been behind a lot of seasoned techs well over my years of experience and have fixed their mistakes time and time again- As well as sub contractors that handle some of our clients when the job is too far to justify driving ( tech expense and fuel costs) Mind you I can see all you guys are great techs no doubts about that. I will take all your guys advice and take sc n sh readings more often.

i would be willing to bet those seasond techs are beer can cold guys too! But glad your hear asking, shows that you are wanting to know. It will take some time to get it down in your troubleshooting, let us know if you have any questions