temp-press for 410a in residential system

[ogre1]

This is my first post in here, and I did search for similar questions, but it may be something that is too basic. Here is the situation.

I have a 410a residential system with a small persistent leak that I am still tracking down. Last summer approx. 1 lb was added to the system to bring it into specification. This summer it again is low on refrigerant. I have 410a refrigerant and a gauge set with dials indicating gauge pressure and 134a temperature. The gauges read gauge pressure to 500 psi and overload to 600-700. I contacted the gauge manufacturer questioning whether I could use the gauges to properly pressurize the system; the response was ambiguous.

Here's my take on it. I can accurately read the ambient temperature, thus I don't need refrigerant temperature values. 410a temperature-pressure charts give me the what the system pressure should be at a certain ambient temp values. Thus, if my gauges read straight gauge pressure (they do), and are rated for the pressures of 410a (they are) I should be able to hook up to the system and add refrigerant unit I reach the table based high- and low-side pressures for the ambient temp at any particular time. Is this correct?

As an aside, that process is how I add 134a to my vehicle, taking ambient temp of the operating environment of the compressor and adding refrigerant until it reaches the specified pressure.

Is this proper or am I waiting on my turn for a "here's your sign reckoning"? Thanks in advance.

[The Viking]

The only way to accurately recharge a modern split system is to reclaim the refrigerant and weigh the correct charge back in.

If you are looking for shortcuts then try searching this board for subcooling or superheat but unfortunately the method you describe in your post will not work.

:cool:

[ogre1]

Viking, thanks.

I do have the capability of evacuating the system if I can find an appropriate recovery tank. Can recovered refrigerant then be measured back into the system (along with additional) to bring it to original specification? What vacuum needs to be pulled?

[peteaddis]

if you need to ask questions about how to correctly charge a system do you not think someone who knows what they are doing should be doing the job instead?

[ogre1]

Pete, not necessarily. The company that installed the system three years ago, with the leak, will no longer service it under warranty period without additional payment. Additionally, the process I described above was the process they used to add refrigerant to the system when I watched last summer. Thus by finding out the information Viking provided I know they are not taking the proper steps in addition to the poor installation. The nearest company other than them has a $150 call-out + $50/lb 410a. So for $200 I am going to find out the necessary steps to do it myself if possible. Though only briefly mentioned above, I have fully serviced, installed and replaced numerous 134a systems. Though that has only been in automobile systems. If it turns out to be too dangerous, or potentially risky to the system, I will do so.

[The MG Pony]

being you have 2 major issues, the leak is the first and it MUST be fixed or you are wasting your time! to do this it must be evacuated, nitrogen purged and braised, to find it you need a leak detector (300 dollars for a cheap one that is reliable) then you need to accurately weigh in the new charge of fresh R-410a, and recheck for any leaks with the sniffer (After doing a 300psi standing nitrogen test for a minimum of 3 hours.

In short just cheaper to get the crew in and just keep an eye and make it obvious you have technical knowledge, it should encourage them to do their job to the fullest! Then it is don with for good, till natural wear and tear bring it down (which should not be any time soon!)

[install monkey]

:confused:weigh it in with scales

[Rob White]

The nearest company other than them has a $150 call-out + $50/lb 410a. So for $200 I am going to find out the necessary steps to do it myself if possible.

The reason why they charge money is because they are trained and have
all the correct tools (which cost thousands to buy), they also have homes
to pay for and families to feed.

Your 134a gauges are not rated for 410a and I'm surprised the manufacturers
were ambiguous with regard to your safty.

Do not use 134a gauges on 410a. 410 at 40degC = 23barg but 134a would be less than 10barg

410 is twice the pressure and you run great risk of hurting yourself.

Rob

.

[ogre1]

Thanks for the replies. I appreciate concern for safety. After speaking with a technician from the manufacturer, I did indeed go the route of superheat / subcool. Thanks for the suggestion Viking. The technician said this is/was an acceptable method. I took this route. Yes, I need to fix the leak but as I mentioned previously, the earlier techs spent several hours looking for it to no avail. One possibility is a tiny leak that will not manifest itself during typ. summer weather, possibly a seal somewhere along the line that moves differentially during our winters, steady state on the system is around 250 or so.

Rob, I looked into the gauge issue further prior to working. The only thing that separates these gauges from standard pressure gauges is the marking on the face and calibration on the low side. They are more than safe for the pressures of 410, they're just marked for 134 (temp). The hoses and body are all standard preassembled equipment with factors of safety above 3.0. The biggest thing to watch for is to ensure no cross contamination (which I was very careful of).

Lastly, I know they have to make money, its the way the world works. But if I have the skill and ability to do something myself, then I typically take that route.

Thanks again for the help and suggestions. I have a properly functioning A/C and just in time too. It was 100+ for about 7 days in a row shortly after I completed the work.