Homemade HC blend (r134a replacement) troubleshooting

[Ben Grimmett]

Afternoon, Sorry for the long post but I feel it may be relevant.

A question that has me puzzled but will be dead simple for most of you.

I have a samsung frostfree fridge/freezer, originally charged with R134a up until the removalists snagged a line at the back during a move a few years ago.

I flushed the system with welding argon/co2 mix and brazed the split as well as added a service port/valve. I pressurised with the argon/co2 to 80psig overnight and found no leaks.

I pulled down a vacuum with a twin stage refrigeration vac pump for about an hour, the gauges I had at the time were not too good so not certain it was free of all moisture but it was a hot day and the vac rattle couldn't be heard so I figured good enough.

I filled with the nameplate weight of r134a and all was well.

Fast forward 2 years and the compressor duty was approaching 100%. I put the gauges on and the suction was running into vacuum. Freezer was still 20 below (C) and fridge was at 4deg but the excessive power consumption was not good for our solar system. Soap water showed the service valve had a very slow leak so it was replaced.

I blended approx 100g of Iso-butane with 190g or propane (welding gasses, not bbq or lab grade etc) I decanted some in a cold beaker and measured -25deg c at atmospheric. This was close to r134a so I proceeded to charge the Samsung until suction pressure was around 4psig. This gave an evap temp of -20degC. I bled off some of the gas and refilled with propane to change the mix and now have -24degc at 4psig.

2 weeks later and the freezer and fridge is working fine, -20deg freezer temp etc.. Duty cycle is 20min on, 45min off and with a 120w compressor this is fine.

The problem is the cycling gurgling noise. After reading through these forum posts it sounds like the refrigerant is flashing in the cap tube. It lasts for about 1 second every 5 seconds. There is no fluctuation of the suction pressure when this happens. It happens regardless of heat load, ambient temp and for the entire cooling cycle. It is best heard beside the freezer compartment where the cap tube enters the suction line.

There is no way to modify the cap tube length, and I don't have a port on the discharge side to monitor. I can purge and refill the refrigerant with varying ratios of propane/iso-butane, as well as increase the suction pressure by overcharging.

My thoughts are, if the propane is flashing off inside the cap tube should I reduce the % of propane in the blend and also reduce the charge to bring the suction pressure down to maintain the -24 evap temp? Or should I keep the % and increase the charge to bring the evap temp down to around -20?

Or is this just a side-effect of using a HC refrigerant in a system designed for 134a?

I am well aware of the risks associated with HC gasses, fire, high pressures, cold etc...

What should I do? Leave it, it's not a problem? Recharge with r134a (rather not), change the blends/pressure?

Thanks!

[BradC]

My experience is HC does make more noise. It's a lot less dense and transports oil considerably better. I found the same thing converting vehicle AC from 134a.

Without replacing the cap tube you'll pretty much have to live with it. Personally I'd recharge it with 134a, and use a new *big* dryer. Any moisture will have started to degrade the lubricant and if you do go back to 134a I'd wager you'll end up with a blocked cap tube unless it's really dry and you are really lucky.

I'd live with it. Probably should have claimed on their insurance and got it replaced

[Magoo]

hello Ben.
I admire your initiative and developing your own blend.
BUT.......! you have gone outside of a lot of legislation requirements for H & S.
Your home and contents insurance cover, public liability cover, are out the window. Apart from putting your family and your self at a huge risk.
Actual components on the actual refrigerator do not comply either as should be sealed and non electrical open contact, ( explosion risk ).
Respectfully suggest using a R290 compatible compressor at least.
just a thought magoo