HVAC gauges

[tonytrakovich]

I am thinking about purchasing a set of gauges so I can top off my own cruisair units. Does any one else do this? What is a good brand / type of gauge? Cost? Can you buy the proper refrigerant? Of course I will read up and learn how to do the maintenance so I don't ruin anything.

[Boatsb]

You top them off after fixing the leak. Therefore if you can't fix it topping them off is just deferred maintenance.

HVAC systems are changing. New gasses are blends and can't be topped off. Old gasses like r22 are becoming expensive and hard to get.

You may find it's not a good time to learn the basics when there's more to it than just filling a system with gas you can't legally buy or use.

[krush]

To legally buy r22 in the usa you need to be certified. This means taking a test (which can be done at many HVAC suppliers). To pass the test, you need to understand and know the theory and some rules. If you are here asking about gauges and refrigerant, you will not past the test without much learning.

Newer units use 410a, which can be bought by anybody (just 134a).....for now. I think this is set to change.

HVAC systems are changing. New gasses are blends and can't be topped off. Old gasses like r22 are becoming expensive and hard to get.

Some blends they say don't top off. Is this just by the book and not practical in the real world??? Potentially.

410a can be topped off.

[Boatsb]

Blends do not leak all components equally. The smaller the molecule the faster it's part can be depleted. If a system is leaking down the remaining refrigerant may not be as efficient as it's ratios are not correct.

[racclarkson@gmail.com]

To legally buy r22 in the usa you need to be certified. This means taking a test (which can be done at many HVAC suppliers). To pass the test, you need to understand and know the theory and some rules. If you are here asking about gauges and refrigerant, you will not past the test without much learning.

I seem to have friends who have gauges that might they want to sell. They always seem call the pro's after they've had a go at AC work.

[Reefgeorge]

A basic Yellow Jacket gauge set works fine, however:

You can't buy most refrigerants without an EPA 608 certification. You take a proctered test at a certified facility. There are four sections related to different types of equipment. You have to pass the general section plus the sections related to your work. Pass all sections and you get a universal certification. You can study for this test with material that you can buy online. Passing this test does not make you good at doing HVAC work but it does sensitize you to good environmental practices and gets you up to speed on refrigerant technology. If you were to get certified keep in mind that many mistakes can be made without proper knowledge. Just adding gas because the low side pressure is low can get you into trouble. Also, once you hook up to a set of service ports you are required to have all of the other equipment to properly service a system (vacuum pumps, reclaim machines, reclaim containers, etc.). Lastly, releasing refrigerant into the atmosphere carries a hefty fine ($28K) and the potential for prison time. The first prison term was given for this in 2014. Point being that it's not a casual DIY project unless you make a commitment.

All that said, if you are technical and a good problem solver, it is doable.

On the issue of blended refrigerants, some fractionate as they leak and the mix can get out of whack and many now require that you charge as a liquid which can trash a compresser from slugging if you are not careful. That said, some of them can be topped off as a liquid and not preturb the system balance to any significant degree. Again, a set of gauges is not enough knowledge.

George

[tonytrakovich]

Thank you George for being the one to answer my question. I have been reading your AC posts lately and you seem to be the resident expert on this. You also have a nice way of explaining things so people can make decisions on the tasks they want to try themselves. Whereas Ill admit that I dont know much about the refrigerant side of AC systems, I would not do anything that has a chance of hurting my equipment or personnel. That being said, I am a better than average DIYer, I can read, and I have the ability to learn. On one of my units, I had a certified AC guy tell me I needed a new compressor. After doing my own troubleshooting I found a bad thermal OL switch on the compressor. I have 7 split systems. All running R22. All evaporators except one are pretty old. I have an old FS30 unit that is original 1989. Also have 5 RX units that were converted to R22. I find it hard to believe that these split systems dont need to be topped off over time. Even if there are no detectable leaks.

[Boatsb]

8 years on one of mine with no need to top it off since I installed it and I live in florida so it gets used.

The older one that is the old blue cruisair I have had the boat for 11 years and it was running when I bought her and still no need to top it off.

[krush]

Thank you George for being the one to answer my question. I have been reading your AC posts lately and you seem to be the resident expert on this. You also have a nice way of explaining things so people can make decisions on the tasks they want to try themselves. Whereas Ill admit that I dont know much about the refrigerant side of AC systems, I would not do anything that has a chance of hurting my equipment or personnel. That being said, I am a better than average DIYer, I can read, and I have the ability to learn.

Well making comments like that are a sure way to ensure that George is the only one to answer your questions.

[Reefgeorge]

There are others with knowledge here for sure and I appreciate all of the information that gets exchanged on this site. I learn a lot from others here.

HVAC systems are designed to hold their refrigerant charge and never need topping off and some systems can run without issue for decades. I have an R22 based residential system that has never needed an ounce of refrigerant after almost 20 years. That said, some systems are more prone to leaking than others. Boats and cars have multiple flared fittings or threaded connections with o rings combined with lots of banging and vibration so even a well installed system can have leaks at the connecting points. Most residential systems are brazed all the way around so any leaks there are usually schrader valves or the evap coil (a growing issue in newer systems). Gauges are the best initial assessment but there are some rule of thumb measurements that give you a lot of information.

Get a baseline delta T by measuring the air temp going into the evaporator and the temp coming out of the vent closest to the evap (if there is more than one). Do this when the cabin air is near the set point so that the humidity is stable. More humidity puts more load on the evaporator heat transfer process and changes everything including gauge pressures. This dela T should be around 20F, mine is 22F. When this starts to drop more than about 2 degrees under similar conditions, something is underperforming. It could be fan efficiency, dirty evap coils, poor heat transfer in the heat exchanger but usually low charge. I use this all the time because it takes 15 seconds with an IR gun. I do put gauges on the system at least once per year but I check this at least once per month.

Also near set point, grab the suction line near the service valve. It should be at least cool and sweating in the summer. Carefully touch the liquid line coming out of the compressor can. It should be hot. The top of the can should be no more than around 250F and most Cruisair units will be considerably less, in the mid to high one hundereds. The process is gas is compressed by the compressor and it gives off heat as the pressure goes up, then the gas is cooled in the condenser coils and in doing so it becomes a liquid and is less hot. This liquid goes to the evap coil where a metering device allows it to expand back into a gas which absorbs heat from the evap fins to complete the phase change. This gas should be slightly cool as it gets back to the compressor but not too much so or the refrigerant may still have some liquid content which is bad. If you like to learn technical stuff look up the ideal gas law which is the law at work in refrigeration.

There are many problems that are not charge related that can be diagnosed with a volt meter, amp clamp meter, and a capacitance meter - all possible with relatively low cost meters these days. The faults can be OL sensors, pressure sensors, capacitors, start relays, cooling water pump relays. You don't need an EPA license to check any of these and some of them fail routinely. All you need is the wiring schematic and some basic knowledge to make sure that the energizing signal is present, the high voltage power is proper, the compressor is getting appropriate power and its running with proper amp draw. BTW another symptom of low charge is lower amp draw. A locked rotor on the other hand has a very high current draw for a few seconds and then goes to zero abruptly as the thermal overload switch opens, only to reset in a minute or two. That spec is actually in the compressor data sheet as well as the normal current draw spec.

Hope that helps.

George