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AC refrigerant low, checking for a leak?


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Hey guys, after a few months, the refrigerant in our mini split unit reduces and the air gets warm. From what I understand, the only cause of this is a leak. We've had 3 different AC repair guys come, they do a routine clean and add refrigerant for around ฿500. Each time we ask them to check for a leak and each time, they plug in a pressure gauge, confirm the refrigerant is low, take a cursory look at the copper tubing, then inform me that there isn't a leak. The last one even charged us ฿200 for this 2 minute facade assessment. They aren't charging the system to 100+PSI and measuring input and return pressure over time. They are not spraying the tubing with soapy water. They claim that a dirty filter, blocked exhaust, etc., is the culprit, but I understand these wouldn't typically cause a drop in refrigerant pressure.

 

So my questions are these: Is my (admittedly limited) understanding about HVAC misinterpreting the situation(s)? Could they deliberately be facilitating a slow leak for repeat business? Or are they lazy and/or incompetent (3 for 3 though, surely this is unlikely)?

 

And finally, anyone ever test for leaks themselves? If so, any areas I should check first other than the brazed joints throughout the line? General estimate on cost of tools? Can I just use a friend's air compressor and spare gauges, or will I need nitrogen specifically? I'd probably want an empty refrigerant tank to collect the refrigerant, then a full one to replace the refrigerant in the purged system right? Thanks, appreciate any advice anyone may have!

 

The unit in question is probably about 4-5 years old and is in use every day. At this use rate, it needs servicing every 6 months(ish). This is an ongoing issue with all of our AC units depending on frequency of use since they were first installed.

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Not the kind of thing you want to take on yourself especially if you don't have the proper equipment.  I suggest calling the service center for the brand and get their qualified technician to check it out.

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A unit that runs everyday, how many BTUs for how big of a room?

Edited by bbko
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5 minutes ago, bbko said:

A mini unit that runs everyday, how many BTUs for how big of a room?

Not 100% on exact measurements, but around 10,000BTU for a 3x3x3m room

 

12 minutes ago, bankruatsteve said:

Not the kind of thing you want to take on yourself especially if you don't have the proper equipment.  I suggest calling the service center for the brand and get their qualified technician to check it out.

I thought this was the DIY forum, not the quitter-talk forum. 😂 kidding

 

Really doesn't seem that hard or expensive though when the same tools and skills can be used over a lifetime.

Edited by ChokDee4213
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6 minutes ago, ChokDee4213 said:

I thought this was the DIY forum, not the quitter-talk forum. Really doesn't seem that hard or expensive when the same tools and skills can be used over a lifetime.

"Quitter-talk forum"?  Interesting observation.

Some jobs should not be attempted with DIY.  Finding and fixing an HVAC leak is one of them.  The fact that you have hired 3 different non-professional repair guys with the same result should tell you something.

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1 minute ago, bankruatsteve said:

"Quitter-talk forum"?  Interesting observation.

Some jobs should not be attempted with DIY.  Finding and fixing an HVAC leak is one of them.  The fact that you have hired 3 different non-professional repair guys with the same result should tell you something.

OK, what should it tell me? What would cause a reduction in refrigerant other than a leak that they are refusing to check for? Please enlighten me, so far your response is just not useful, I'm sorry.

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A simple pressure test tells you nothing about the amount of refrigerant in your system. A refrigerant gas tester is not cheap if it’s any good, the training to know where to test and how to test is needed to use it, and even if you locate a leak the skill to repair or knowledge that it can’t be fixed is needed

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2 minutes ago, ChokDee4213 said:

OK, what should it tell me? What would cause a reduction in refrigerant other than a leak that they are refusing to check for? Please enlighten me, so far your response is just not useful, I'm sorry.

You already know that they are not competent AC mechanics so why should they be correct that your refrigerant is low?

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Just now, sometimewoodworker said:

You already know that they are not competent AC mechanics so why should they be correct that your refrigerant is low?

I didn't know that and was asking for confirmation on that point. 3 for 3 are pretty incredible odds for incompetency.

 

Just out of curiosity, does anyone here have experience with HVAC that can comment on the situation with a little less conjecture? If not, that fine, thanks for your time.

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35 minutes ago, ChokDee4213 said:

Could they deliberately be facilitating a slow leak for repeat business? Or are they lazy and/or incompetent (3 for 3 though, surely this is unlikely)?

 

And finally, anyone ever test for leaks themselves? If so, any areas I should check

Yes many will not even try to find a leak  they just want to come and top up the coolant...sometimes finding and fixing the leak would mean removing the whole aircon unit and perhaps taking it to their workshop to do welding/brazing  then pressure test then bring it all back and basically do another full reinstall...lots of work for them customer without aircon for at least a day and night.

One thing you can quite easily check are the Schrader valves   these are where they connect the measuring gauges..the Schrader valves should also have a cover on them which can help stop leaks...mine have been good for the last couple of years after I happened upon a aircon fixerer

that suggested the valve was leaking and used ptfe tape to make the brass cover an extra barrier to leaks.

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1 minute ago, ChokDee4213 said:

I didn't know that and was asking for confirmation on that point. 3 for 3 are pretty incredible odds for incompetency.

Not really. There are many “technicians” here with no technical training, so 3 for 3 unless they are from the manufacturer is normal 

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When the refrigerant starts to get low, the evaporator coil should start frosting/freezing over. Is this happening? 

 

Air-conditioners do not "use" refrigerant, if it is low, it is leaking.

 

Leaks that are not relatively obvious can be hard to find and are often difficult to fix. 

 

Is the coil aluminum or copper? 

 

 

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8 hours ago, Yellowtail said:

When the refrigerant starts to get low, the evaporator coil should start frosting/freezing over. Is this happening? 

 

Air-conditioners do not "use" refrigerant, if it is low, it is leaking.

 

Leaks that are not relatively obvious can be hard to find and are often difficult to fix. 

 

Is the coil aluminum or copper? 

 

 

Difficult to say, I haven't checked it directly and it's too late now that the technician just added refrigerant. I am hoping the coils are not the issue given that they were just recently replaced less than a year ago. There was no condensation coming from the unit inside the house itself if that's an indicator. The coil is copper.

 

The return line was noticeably warmer prior to the technician's visit as well if that helps, but I didn't record exact temperature change.

 

Someone above said that I cannot check if there is a leak by purging the system, taking it to 100PSI and measuring any drop off, is that true? If so, I think the best I can do is spray soapy water on the connection manifold and copper lines external to the compressor, but it could be a wild-goose chase. I imagine checking the coils specifically involves removing and submerging them and I might be better off just contacting the guy that recently replaced it.

Edited by ChokDee4213
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7 hours ago, ChokDee4213 said:

Difficult to say, I haven't checked it directly and it's too late now that the technician just added refrigerant. I am hoping the coils are not the issue given that they were just recently replaced less than a year ago. There was no condensation coming from the unit inside the house itself if that's an indicator. The coil is copper.

 

7 hours ago, ChokDee4213 said:

Someone above said that I cannot check if there is a leak by purging the system, taking it to 100PSI and measuring any drop off, is that true?

Neither of those ways are correct. 
the correct way is to first use a gas sniffing tool to locate a possible leak, then use a detergent containing liquid in the area that gas was detected if it was, then recover the charge finding the weight recovered, flow nitrogen through the system to stop contamination, solder the leaks, pull the system down to as near a vacuum as is recommended (you will have gas dissolved in the compressor oil so the vacuum is limited) over about 10 to 30 minutes confirm that the vacuum decay is low enough that it’s only due to dissolved gas, then finally put the correct weight of refrigerant back in.

 

soapy water is a poor choice as you need a bubble free liquid on the AC .

So how many AC cleaning techs here have the equipment to actually do that, even in their shop? And a leak must be found in the installed AC.

Edited by sometimewoodworker
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7 hours ago, ChokDee4213 said:

Difficult to say, I haven't checked it directly and it's too late now that the technician just added refrigerant. I am hoping the coils are not the issue given that they were just recently replaced less than a year ago. There was no condensation coming from the unit inside the house itself if that's an indicator. The coil is copper.

 

The return line was noticeably warmer prior to the technician's visit as well if that helps, but I didn't record exact temperature change.

 

Someone above said that I cannot check if there is a leak by purging the system, taking it to 100PSI and measuring any drop off, is that true? If so, I think the best I can do is spray soapy water on the connection manifold and copper lines external to the compressor, but it could be a wild-goose chase. I imagine checking the coils specifically involves removing and submerging them and I might be better off just contacting the guy that recently replaced it.

You have a unit that is only 4-5 years old and have apparently had to replace both coils after only 3-4 years, and have had several techs out since then? 

 

Why would you not call the that changed the coils out to start with if it was still leaking? 

 

What happened to the dealer you bought it from?

 

What brand is the unit? I would think about getting the manufacturer involved.

 

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33 minutes ago, sometimewoodworker said:

 

Neither of those ways are correct. 
the correct way is to first use a gas sniffing tool to locate a possible leak, then use a detergent containing liquid in the area that gas was detected if it was, then recover the charge finding the weight recovered, flow nitrogen through the system to stop contamination, solder the leaks, pull the system down to as near a vacuum as is recommended (you will have gas dissolved in the compressor oil so the vacuum is limited) over about 10 to 30 minutes confirm that the vacuum decay is low enough that it’s only due to dissolved gas, then finally put the correct weight of refrigerant back in.

 

soapy water is a poor choice as you need a bubble free liquid on the AC .

So how many AC cleaning techs here have the equipment to actually do that, even in their shop? And a leak must be found in the installed AC.

Dye testing is nice as well as it is better for finding small  and multiple leaks, and stays in the system helping to find future leaks.

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3 hours ago, Yellowtail said:

Dye testing is nice as well as it is better for finding small  and multiple leaks, and stays in the system helping to find future leaks.

Dye added to refrigerant can certainly help in some cases and has its uses. Maybe for the OP since he can’t seem to find an actual AC repair technician.

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