D4 A/C Compressor issue

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28th December 2022, 10:19 AM
BradC

Quote:

Originally Posted by haydent

the tech said the gas amount was ok when he tested it when it wasnt working initially (due to siezed and broken pulley)

The only way to do that is to pull the gas out and weigh it. Did the Natrad guy do that?

Quote:

Originally Posted by haydent

why would it be in the evaporator and not the condenser ? because as the liquid evaporates it leaves the oil behind ?

Bang on. In a fully charged system there is enough vigorous boiling in the evap to spit the oil out the suction line, but as the refrigerant level drops that reduces until the evap gets oil logged, the compressor is starved of oil and it lunches itself.

It's why I always bang on about the "periodic regas". All systems leak. Even fully brazed hermetic systems leak. It's the leak rate that differs. These systems have a rotating seal on the compressor and elastomer seals on every joint. They *all* leak.
28th December 2022, 10:28 AM
haydent

Quote:

Originally Posted by BradC

The only way to do that is to pull the gas out and weigh it. Did the Natrad guy do that?

I dont think so, could you not tell by just testing the idle system pressure ? Thats how a diving tank measures time left...

Quote:

Originally Posted by BradC

Bang on. In a fully charged system there is enough vigorous boiling in the evap to spit the oil out the suction line, but as the refrigerant level drops that reduces until the evap gets oil logged, the compressor is starved of oil and it lunches itself.

very likely, still thinking about that dash, maybe, maybe not. might put the pump back in (lines disconnected) while i think.
28th December 2022, 11:17 AM
DiscoJeffster

Quote:

Originally Posted by haydent

I dont think so, could you not tell by just testing the idle system pressure ? Thats how a diving tank measures time left...

very likely, still thinking about that dash, maybe, maybe not. might put the pump back in (lines disconnected) while i think.

The forty hours to get that Evap out to replace the TX. No one would ever do this unless the Evap sprung a leak, right or wrong. That video I posted earlier shows the complete process.
28th December 2022, 11:24 AM
BradC

Quote:

Originally Posted by haydent

I dont think so, could you not tell by just testing the idle system pressure ? Thats how a diving tank measures time left...

A diving tank stores compressed air. A refrigeration system stores refrigerant. They are not the same. At all times there is supposed to be liquid refrigerant in the system. Whether there is 1ml or 100L the pressure will be the same at the same temperature. Completely, totally and utterly different. You can not tell how much refrigerant is in a system by measuring the static pressure.

Can you tell how much gas is left in your 9KG gas bottle by measuring the pressure? No. Same reason.
28th December 2022, 11:38 AM
haydent

Quote:

Originally Posted by DiscoJeffster

The forty hours to get that Evap out to replace the TX. No one would ever do this unless the Evap sprung a leak, right or wrong. That video I posted earlier shows the complete process.

That was a good (but scary) video thanks. Im definately not contemplating that, just maybe a dash only to get to the tx.

Quote:

Originally Posted by BradC

A diving tank stores compressed air. A refrigeration system stores refrigerant. They are not the same. At all times there is supposed to be liquid refrigerant in the system. Whether there is 1ml or 100L the pressure will be the same at the same temperature. Completely, totally and utterly different. You can not tell how much refrigerant is in a system by measuring the static pressure.

Can you tell how much gas is left in your 9KG gas bottle by measuring the pressure? No. Same reason.

Well you can got a rough idea, I have pressure gauges for my gas bottles that have dials. I had a google and found this Why Can’t You Just Measure Pressures to Check a Refrigerant Charge? so maybe he did it that way. I will ask him tommorow.
28th December 2022, 12:02 PM
BradC

Quote:

Originally Posted by haydent

Well you can got a rough idea, I have pressure gauges for my gas bottles that have dials. I had a google and found this Why Can’t You Just Measure Pressures to Check a Refrigerant Charge? so maybe he did it that way. I will ask him tommorow.

No you can't. You can get "gas or no gas". r134a at 25C is 1.206kg/L. The system holds ~600g. That's ~497ml. Whether it's that, or there's 1ml left the pressure will be the same.

He'd be a bloody good tech if he can do a superheat or subcooling measurement on a system with a lunched compressor.
28th December 2022, 12:19 PM
gavinwibrow

Quote:

Originally Posted by BradC

It's why I always bang on about the "periodic regas". All systems leak. Even fully brazed hermetic systems leak. It's the leak rate that differs. These systems have a rotating seal on the compressor and elastomer seals on every joint. They *all* leak.

Maybe I've missed it but can you provide a bit more detail on periodic regas please (timelines etc)? I've often wondered why this is not a regular maintenance item, particularly given the problems/costs with total replacement/s.
28th December 2022, 12:35 PM
RANDLOVER

https://www.aulro.com/afvb/images/misc/quote_icon.png Originally Posted by BradC https://www.aulro.com/afvb/images/bu...post-right.png
It's why I always bang on about the "periodic regas". All systems leak. Even fully brazed hermetic systems leak. It's the leak rate that differs. These systems have a rotating seal on the compressor and elastomer seals on every joint. They *all* leak.

Quote:

Originally Posted by gavinwibrow

Maybe I've missed it but can you provide a bit more detail on periodic regas please (timelines etc)? I've often wondered why this is not a regular maintenance item, particularly given the problems/costs with total replacement/s.

I agree everything leaks, similar to Dr House's motto of "everybody lies" House (TV series) - Wikipedia. Not sure on timelines but as soon as mine had a few of struggling to cool episodes I got my a/c gas topped up, following advice on this forum about the gas carrying oil around the system, basically they vacuum it out, weigh it, top it up and re-insert it in the system. Mine was missing quite a bit, and is noticeably colder now, can actually cause pain in my hands if the vents are directed at them.

Older shaft seals were notorious for leaking in winter when the a/c wasn't used, so manufacturers came up with all sorts of ideas to run the units, on timers, when reverse was engaged, etc.
28th December 2022, 12:37 PM
scarry

Quote:

Originally Posted by LuckyLes

The difference between an auto car system and a commercial system is accessibility of the components. If he gets to the recharge point and finds that the TX is blocked or jammed, basically he has to start again.

Exactly,who wants to pull it out if they don’t have to.

That is why I would give it a crack,that is flush with the valve in place.Do it from as close to the inlet of the valve as possible,to minimise the rubbish that goes into it.Any rubbish downstream of the drier is going to go into it anyway,once the system is operational.

As said,we have done it before on systems with TX and other types of expansion valves and had success.
Access to some of the expansion devices on systems we work on is also extremely difficult.
Takes a bit of time,and higher pressure.
Using shellite,as we do,once liquid shellite comes out the suction,clean,it is just about done.

Still better than not having a go.
Anyway each to their own.
28th December 2022, 12:46 PM
scarry

Quote:

Originally Posted by BradC

If it has been running with low refrigerant the missing oil is probably in the evaporator, which is another reason it really needs to be flushed.

That is exactly what happened to that 30 KW AC system we sorted last week.We flushed 4.5L of black oil out of the evap.
Low on refrigerant,low pressure switch not working,etc,etc.

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