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dannnyboy · May 21, 2009, 03:21 PM

Hi,
I have a split 12,000btu AC unit running on R407c gas. It was a DIY install last year.
When first installed it worked perfectly.
I had a small leak where one of the connections which was not done up tight enough. Once I noticed a mark on the wall where the gas had leaked and left a mark I tightened up the connection and since no more gas has leaked.
My problem is the AC unit is no longer as cold as when it was first installed.
I have done a lot of research on how to top up the gas and understand I need to get a set of gauges with the blue being connected to the low pressure (Large pipe) and the red to the High pressure (Smaller pipe) leaving me with the yellow pipe to connect to the bottle.
My question is how much gas do I put in?
I take it I connect the gauges and take a reading then add enough gas to fill the system back up?
Can anyone help me with what pressure I need to have?
Do I need to run the unit before filling up with gas like the descriptions seem to indicate with cars?

Any help or advice would be gratefully received

Kind Regards

Dannny

mygirlsdad77 · May 21, 2009, 03:40 PM

Danny, you need to be licensed to work with refrigerant. You have a leak, it needs to be located and fixed before adding more refrigerant. I would suggest having a licensed ac tech in to look at your system. I really wish I could help you with this one, but I'm afraid you won't get any better answers on this site. This one is best left to the pros. Good luck, and please let us know how things turn out.

dannnyboy · May 22, 2009, 01:19 AM

Hi,

mygirlsdad77, I am in the UK. As I said in my post the leak is fixed the temperature is still cooler than ambient just not as cool as it should be.
I did contact some `pros` however to me the prices I have been quoted seems to be daylight robbery. I have prices ranging from £300 to £450 just to put gas in the system.

dac122 · May 22, 2009, 05:57 AM

You have found and fixed the leak so that is an important part. As you have already suspected you have lost some charge and therefore the system is running well below its cooling capacity.

This is a borderline DIYer project if you are willing to educate yourself on the proper procedure of charging by superheat and subcool. Search on those terms to charge a system, and get the manufacturers procedure to tweak it for peak efficiency. You have the general procedure down, except the unit must be running and reach steady state before charging.

While those costs my seem high, you may be getting a little more than just gas and go as they may also do a general system checkup. By comparison, the cost to do it yourself, you will need several pounds of refrigerant, gauges for that refrigerant and accurate temperature probes. There is also the risk if you overcharge the system you can damage the compressor. Finally, I have not idea what regulations govern buying and handling refrigerant in the UK. I'm not trying to talk you out of this, but do your homework and do a little cost/benefit/risk analysis before you decide to do this yourself.

mygirlsdad77 · May 22, 2009, 03:37 PM

Not sure on UK guedelines for licensing either, but I'm pretty sure it's a global thing. I know you fixed the large leak that was noticeable from the oil that sprayed on the wall, but there may be another very small leak that can't be found without a tester or soap and water. If you are allowed to do this yourself, one easy way to do it is to reclaim all refrigerant(wich requires a reclaim machine and bottle) then pull a vacuum on the system(wich requires a vacuum pump), then if you have a very very accurate scale, you can just charge the system with the correct amount of refrigerant. The unit will have a label on it that has model no, serial no, so on so forth.. On this label, you will find the factory charge of the system. If you get all refrigerant out, then you will only need to put in the required factory charge(unless you line set is very long, in wich case there should be a table in the install istructions as to how much extra refrigerant need to be added)

Not sure about the difference in currency from uk to us, so I can't say for sure whether or not the pros are asking too much. Please let me know how things work out.