R290 undercharge in 1 ton cap tube split sytem heat pump?

r290r600 · 12-22-13, 10:39 PM

Hi all,
I have a 1 ton (2.4kw) cap tube split system which was originally on R410a until the old gas escaped after a copper line failed....since the system was open to atmosphere i decided to plumb in a reversible filter dryer in the liqiud line to catch any moisture etc. After doing a fair bit of reading and cosideration I have decided to regas the system with R290. According to the literature the charge is 40% (304g) of the original 760 grams...no problem there but was unable to get the specs on the liquid capacity of the filter...comparing it with some similar models of filter I estimated that the filter capacity with R290 was around 50 grams. So after making sure the system was leak proof and evacuated, I put my charge in and tried the system. Tried it on cool and no cold air...this ststem only has a service port on the low side and was reading around 20psi...the liquid line felt very cool....reading some another post on the Refigeration Engineer forum re R290 i should be reading 63-70 psi on the low side. My assumption is that I am undercharged and i will need to add small amounts of refrigerant until i get a good vent temp at the evaporator.
Thanks!

NiHaoMike · 12-22-13, 10:47 PM

Add a sight glass and a R22 TXV.

AC_Hacker · 12-23-13, 01:10 AM

Quote:

Originally Posted by r290r600

...but was unable to get the specs on the liquid capacity of the filter...comparing it with some similar models of filter I estimated that the filter capacity with R290 was around 50 grams...

I think that if you make major changes to the volume of the system, it's just too complicated to charge by weight.

It's a lot nicer if you have a hi-side Schrader valve AND a lo-side Schrader valve.

My systems began to make beautiful frost at around hi-side = 140 to 150 psi and low side around 40 to 60 psi.

Somehow, I usually managed to over fill the systems and had to bleed a bit out before it really started working... then maybe add a bit or bleed a bit until it's performance is maximized. Since R290 has zero potential for either global warming OR ozone destruction (the basis of the EPA laws), you should be able to live with your conscience. But be mindful any flame or spark!!! (including relays)

BTW, when you make an adjustment, one way or the other, let it run for 10 minutes minimum so that things "settle in" before you make a change in charge.

Good luck, you're almost there.

-AC

jeff5may · 12-23-13, 01:18 AM

You can try to balance your system by adding R290, but with a metering device made for R410, the system will never run at high efficiency unless you recharge it with R410a. The engineers put an exraordinary amount of design and testing into sizing cap tubes for a particular refrigerant. Just a centimeter of difference in the length makes a big change.

If you are planning on running R290 anyways, you can make it do something with the cap tube that's in there by charging using suction superheat. First, make sure the system has been evacuated deeply. Add refrigerant from the low side port (slowly) until the whole system is around 50 Psi gauge reading. An easy way to do this is to put your R290 canister in an ice water bath and slowly add gas at first. Once you get to around 40Psi, open the valve on your gauge set up and let the gas flow slowly into the high side. Wait awhile until the pressure equalizes.

Once the gas has stopped flowing from your canister, close the valve on your gauge set, take the canister out of the ice bath, and start the compressor. When the low side pressure drops, add gas by cracking the gauge valve open. As liquid builds up on the high side, your low side pressure will rise and fall wildly as the liquid is exhausted and gas flows thru the cap tube.

At some point, enough liquid will back up to support a solid stream of refrigerant to flow into the cap tube. Your evaporator coil will start to cool and frost up at this point. Using a digital thermometer, measure the temperature of the refrigerant line close to where it leaves the evaporator. If it isn't cold, continue to add refrigerant slowly until it gets cold. If the evaporator frosts up enough to block airflow, close the gauge valve, shut off the compressor, and wait until the evaporator thaws out.

Once your evaporator leaving line cools, you can begin taking superheat measurements. For ballpark estimation, you can use the R22 scale on your gauge to obtain Saturated Suction Temperature. As you add refrigerant, the SST will rise. Compare the thermometer reading with the SST, the difference is your suction superheat. With a cap tube system, you want to always have at least 10-15 degC of suction superheat.

As you add refrigerant, keep an eye on the superheat. Too little superheat and your compressor can flood. When you stop filling, the pressure will drop and then level off. Take a superheat reading. If it's sky high or your evap coil is frosting, add a little more gas. At a certain point, it will take a long time for the pressure to drop, and the evap will stop frosting up. Your ending SST will depend on a zillion things, but should be above freezing if it is warm outside (above 25-30 degC).

mejunkhound · 12-23-13, 09:33 AM

Quote:

Originally Posted by NiHaoMike

Add a sight glass and a R22 TXV.

+1

plus, if you used bbq propane for R290, and the 410 system did have a cap tube, just the 10 ppm of water in bbq propane may be enough to freeze a slug of ice in the cap tube.

TXV will recoup it's cost within months.

r290r600 · 12-23-13, 04:27 PM

I did use BBQ propane which according to the suppliers data sheet is more than 95-99% propane and 1-5% ethane. I passed it through a filter drier first to remove as much moisture as possible. Also there is the reversible filter drier in the liquid line.

r290r600 · 12-23-13, 04:41 PM

Hi all, thanks for your replies.
A couple of questions -
To get the system working I know it is better, but can I still get my charge right without having a schrader valve in the high side?
When adding refrigerant to the suction line and having the R290 canister in an ice bath, my canister will have the valve at the top (obviously!) and I will be charging as gas not liquid. To filter the moisture out I assume that my liquid line filter I used previously will now be ineffective and i would need to use a suction line filter.
Thanks once again and Happy Holidays to you all.

NiHaoMike · 12-23-13, 05:26 PM

You'll need high side access to do it right. While you're at it, you can also add in the TXV (two plus check valves for a heat pump) and sight glass. The old cap tube is not going to work very well with R290.

WyrTwister · 12-24-13, 10:32 AM

Around here R410a may be purchased w/o an EPA card ( I do have an EPA card , I still have a R22 unit to support ) .

So , I would use R410a and be done with it . That is what my ductless mini split uses .

God bless
Wyr

r290r600 · 12-26-13, 04:37 AM

I can not buy R410A in Australia cause i am not a refrig tech and am not frieinds with any refrig techs and if I could purchase R410a is only available in large and expensive cylinders.....that is why I am attempting to use R290

12-22-13, 10:39 PM	#1
r290r600 Lurking Renovator Join Date: Dec 2013 Location: Victoria, Australia Posts: 19 Thanks: 5 Thanked 0 Times in 0 Posts	R290 undercharge in 1 ton cap tube split sytem heat pump? Hi all, I have a 1 ton (2.4kw) cap tube split system which was originally on R410a until the old gas escaped after a copper line failed....since the system was open to atmosphere i decided to plumb in a reversible filter dryer in the liqiud line to catch any moisture etc. After doing a fair bit of reading and cosideration I have decided to regas the system with R290. According to the literature the charge is 40% (304g) of the original 760 grams...no problem there but was unable to get the specs on the liquid capacity of the filter...comparing it with some similar models of filter I estimated that the filter capacity with R290 was around 50 grams. So after making sure the system was leak proof and evacuated, I put my charge in and tried the system. Tried it on cool and no cold air...this ststem only has a service port on the low side and was reading around 20psi...the liquid line felt very cool....reading some another post on the Refigeration Engineer forum re R290 i should be reading 63-70 psi on the low side. My assumption is that I am undercharged and i will need to add small amounts of refrigerant until i get a good vent temp at the evaporator. Thanks!

12-22-13, 10:47 PM	#2
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	Add a sight glass and a R22 TXV. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

12-23-13, 01:18 AM	#4
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,428 Thanks: 431 Thanked 619 Times in 517 Posts	You can try to balance your system by adding R290, but with a metering device made for R410, the system will never run at high efficiency unless you recharge it with R410a. The engineers put an exraordinary amount of design and testing into sizing cap tubes for a particular refrigerant. Just a centimeter of difference in the length makes a big change. If you are planning on running R290 anyways, you can make it do something with the cap tube that's in there by charging using suction superheat. First, make sure the system has been evacuated deeply. Add refrigerant from the low side port (slowly) until the whole system is around 50 Psi gauge reading. An easy way to do this is to put your R290 canister in an ice water bath and slowly add gas at first. Once you get to around 40Psi, open the valve on your gauge set up and let the gas flow slowly into the high side. Wait awhile until the pressure equalizes. Once the gas has stopped flowing from your canister, close the valve on your gauge set, take the canister out of the ice bath, and start the compressor. When the low side pressure drops, add gas by cracking the gauge valve open. As liquid builds up on the high side, your low side pressure will rise and fall wildly as the liquid is exhausted and gas flows thru the cap tube. At some point, enough liquid will back up to support a solid stream of refrigerant to flow into the cap tube. Your evaporator coil will start to cool and frost up at this point. Using a digital thermometer, measure the temperature of the refrigerant line close to where it leaves the evaporator. If it isn't cold, continue to add refrigerant slowly until it gets cold. If the evaporator frosts up enough to block airflow, close the gauge valve, shut off the compressor, and wait until the evaporator thaws out. Once your evaporator leaving line cools, you can begin taking superheat measurements. For ballpark estimation, you can use the R22 scale on your gauge to obtain Saturated Suction Temperature. As you add refrigerant, the SST will rise. Compare the thermometer reading with the SST, the difference is your suction superheat. With a cap tube system, you want to always have at least 10-15 degC of suction superheat. As you add refrigerant, keep an eye on the superheat. Too little superheat and your compressor can flood. When you stop filling, the pressure will drop and then level off. Take a superheat reading. If it's sky high or your evap coil is frosting, add a little more gas. At a certain point, it will take a long time for the pressure to drop, and the evap will stop frosting up. Your ending SST will depend on a zillion things, but should be above freezing if it is warm outside (above 25-30 degC). Last edited by jeff5may; 12-23-13 at 01:21 AM..

12-23-13, 05:26 PM	#8
NiHaoMike Supreme EcoRenovator Join Date: Oct 2008 Location: Austin, TX Posts: 1,154 Thanks: 14 Thanked 257 Times in 241 Posts	You'll need high side access to do it right. While you're at it, you can also add in the TXV (two plus check valves for a heat pump) and sight glass. The old cap tube is not going to work very well with R290. __________________ To my surprise, shortly after Naomi Wu gave me a bit of fame for making good use of solar power, Allie Moore got really jealous of her...

12-23-13, 04:27 PM	#6
r290r600 Lurking Renovator Join Date: Dec 2013 Location: Victoria, Australia Posts: 19 Thanks: 5 Thanked 0 Times in 0 Posts	I did use BBQ propane which according to the suppliers data sheet is more than 95-99% propane and 1-5% ethane. I passed it through a filter drier first to remove as much moisture as possible. Also there is the reversible filter drier in the liquid line.

12-23-13, 04:41 PM	#7
r290r600 Lurking Renovator Join Date: Dec 2013 Location: Victoria, Australia Posts: 19 Thanks: 5 Thanked 0 Times in 0 Posts	Hi all, thanks for your replies. A couple of questions - To get the system working I know it is better, but can I still get my charge right without having a schrader valve in the high side? When adding refrigerant to the suction line and having the R290 canister in an ice bath, my canister will have the valve at the top (obviously!) and I will be charging as gas not liquid. To filter the moisture out I assume that my liquid line filter I used previously will now be ineffective and i would need to use a suction line filter. Thanks once again and Happy Holidays to you all.

12-24-13, 10:32 AM	#9
WyrTwister Master EcoRenovator Join Date: Jun 2013 Location: USA Posts: 543 Thanks: 6 Thanked 44 Times in 38 Posts	Around here R410a may be purchased w/o an EPA card ( I do have an EPA card , I still have a R22 unit to support ) . So , I would use R410a and be done with it . That is what my ductless mini split uses . God bless Wyr

12-26-13, 04:37 AM	#10
r290r600 Lurking Renovator Join Date: Dec 2013 Location: Victoria, Australia Posts: 19 Thanks: 5 Thanked 0 Times in 0 Posts	I can not buy R410A in Australia cause i am not a refrig tech and am not frieinds with any refrig techs and if I could purchase R410a is only available in large and expensive cylinders.....that is why I am attempting to use R290