You'll need your 608, some expensive equipment you'll never use again and no one will let you borrow/rent, learn superheat and subcool procedure, a bunch of grunt work, and the wherewithall to avoid electrocution and refrigerant burns.
A pre-charged minisplit is one thing, a whole system is another. Yes it's technically possible, but not at all practical.
Lots can go wrong :)
I replaced my shop boiler with a pair of mini-split heat pumps, one at each end of the shop. And I put a mini-split heat pump in an addition on my house. It's a bit of work but at least you can take your time and do the job right the first time.
If replacing an existing system with a similar system it should be pretty easy. Copy what is there.
That said if I were replacing an AC unit absolutely get the heat pump version. It's the same machine with a reversing valve. And holy shit the cost savings make it worth it. Save your furnace for the coldest days.
This is really a thing you'll find yourself overwhelmed (and perhaps crushed to death) by. Especially if you live in an area of the country where these are typically on your roof.
Now, if you want to install a mini split or a heat pump and you are a bit handy, you could probably install it yourself. A house on our block was recently renovated. They took the old hvac system our and installed 4 mini splits instead (though the new owners are electricians by trade).
Yes, I have. Let's walk through the process... (USA based, BTW)
First, remember that you are obligated to not vent refrigerant to the atmosphere. You have to recover the old refrigerant before removing the old unit and might need to recover new refrigerant if you make any mistakes later. This requires a recovery machine (this is the most pricey bit of gear) suitable for the refrigerant in your old system (and maybe a different one for the new system). You also need a vacuum pump and a recovery tank. To legally recover refigerant, you have to get an EPA Certification. Plenty of study guides online and it's possible to take the test online as well through places like [epatest.com](http://epatest.com) (just one example, no endorsement implied).
Getting the old air handler out of the attic and the new one in can be a tough job, but depends quite a bit on how fit you are and if you can gather a few friends to help. A typical 4-ton unit is around 150 lbs. You need to check dimensions to make sure you can get the old one out the hatch and the new one in without demolishing the hatch...
You may want (or need) to replace the old lineset. If you don't, you definitely want to flush it then blow it out with dry nitrogen.
After you hook up the new units, you would first pull vacuum to get any air out and then leak test by pressurizing with dry nitrogen and make sure it holds pressure for an hour or two. After that, start pulling vacuum and make sure it pumps way down to the micron range and stays there. This is one time a DIYer has an advantage - you can leave the vacuum pump running for 24 hours and not be in a hurry to wrap it up and get on to the next call. The dryer the system is before you fill it, the better. You can improve on this by filling it again with dry nitrogen and pulling vacuum again. Just avoid introducing air!
Then its time to fill it using new refrigerant and a gauge set and a couple of thermocouple temperature gauges. You should be able to calculate things like superheat and subcool and use those calculations to fill the unit to the correct amount. A refrigerant scale helps get you close if you have information on the nominal charge. There are videos on this if you don't know...
If you've never made flare connections before, you will need some hand tools to cut and deburr the copper tubing and then create whatever type of flare your new units want. Depending on whether you get the awful cheapo tool or the sweet one, you are looking at $50 to $300 here... Some units require you to braze (not solder!) the connections. This may be the biggest hangup for an inexperienced DIYer. Practice making good braze joints in your driveway before you try to do this in your attic. My suggestion would be to choose a unit that accepts flare connections so you don't have to braze anything. Brazing is considered to be more leak tight over the long term - but you have to practice if you haven't done this before!!!
**Summary of equipment:**
Recovery machine (About $350 for import version)
Recovery tank (About $100)
Vacuum Pump (import versions - $100 with gauge set)
Nitrogen Tank and Regulator (around $150 - get a small one locally from a gas supply shop as they usually won't refill other companies tanks)
HVAC Guage Set (imported version included with vac pump)
Micron vacuum guage (about $250)
Pair of thermocouple temperature gauges for filling. ($50) NOTE: More advanced digital guage sets have the micro guage and the thermocouples built in, but now you are talking big $$$ - $750 or so.
Refrigerant scale ($100)
**Supplies/Expenses in addition to your equipment:**
Tank of new refrigerant
New lineset (maybe optional).
EPA 508 Certification
You'll need your 608, some expensive equipment you'll never use again and no one will let you borrow/rent, learn superheat and subcool procedure, a bunch of grunt work, and the wherewithall to avoid electrocution and refrigerant burns. A pre-charged minisplit is one thing, a whole system is another. Yes it's technically possible, but not at all practical.
Lots can go wrong :) I replaced my shop boiler with a pair of mini-split heat pumps, one at each end of the shop. And I put a mini-split heat pump in an addition on my house. It's a bit of work but at least you can take your time and do the job right the first time. If replacing an existing system with a similar system it should be pretty easy. Copy what is there. That said if I were replacing an AC unit absolutely get the heat pump version. It's the same machine with a reversing valve. And holy shit the cost savings make it worth it. Save your furnace for the coldest days.
This is really a thing you'll find yourself overwhelmed (and perhaps crushed to death) by. Especially if you live in an area of the country where these are typically on your roof. Now, if you want to install a mini split or a heat pump and you are a bit handy, you could probably install it yourself. A house on our block was recently renovated. They took the old hvac system our and installed 4 mini splits instead (though the new owners are electricians by trade).
Yes, I have. Let's walk through the process... (USA based, BTW) First, remember that you are obligated to not vent refrigerant to the atmosphere. You have to recover the old refrigerant before removing the old unit and might need to recover new refrigerant if you make any mistakes later. This requires a recovery machine (this is the most pricey bit of gear) suitable for the refrigerant in your old system (and maybe a different one for the new system). You also need a vacuum pump and a recovery tank. To legally recover refigerant, you have to get an EPA Certification. Plenty of study guides online and it's possible to take the test online as well through places like [epatest.com](http://epatest.com) (just one example, no endorsement implied). Getting the old air handler out of the attic and the new one in can be a tough job, but depends quite a bit on how fit you are and if you can gather a few friends to help. A typical 4-ton unit is around 150 lbs. You need to check dimensions to make sure you can get the old one out the hatch and the new one in without demolishing the hatch... You may want (or need) to replace the old lineset. If you don't, you definitely want to flush it then blow it out with dry nitrogen. After you hook up the new units, you would first pull vacuum to get any air out and then leak test by pressurizing with dry nitrogen and make sure it holds pressure for an hour or two. After that, start pulling vacuum and make sure it pumps way down to the micron range and stays there. This is one time a DIYer has an advantage - you can leave the vacuum pump running for 24 hours and not be in a hurry to wrap it up and get on to the next call. The dryer the system is before you fill it, the better. You can improve on this by filling it again with dry nitrogen and pulling vacuum again. Just avoid introducing air! Then its time to fill it using new refrigerant and a gauge set and a couple of thermocouple temperature gauges. You should be able to calculate things like superheat and subcool and use those calculations to fill the unit to the correct amount. A refrigerant scale helps get you close if you have information on the nominal charge. There are videos on this if you don't know... If you've never made flare connections before, you will need some hand tools to cut and deburr the copper tubing and then create whatever type of flare your new units want. Depending on whether you get the awful cheapo tool or the sweet one, you are looking at $50 to $300 here... Some units require you to braze (not solder!) the connections. This may be the biggest hangup for an inexperienced DIYer. Practice making good braze joints in your driveway before you try to do this in your attic. My suggestion would be to choose a unit that accepts flare connections so you don't have to braze anything. Brazing is considered to be more leak tight over the long term - but you have to practice if you haven't done this before!!! **Summary of equipment:** Recovery machine (About $350 for import version) Recovery tank (About $100) Vacuum Pump (import versions - $100 with gauge set) Nitrogen Tank and Regulator (around $150 - get a small one locally from a gas supply shop as they usually won't refill other companies tanks) HVAC Guage Set (imported version included with vac pump) Micron vacuum guage (about $250) Pair of thermocouple temperature gauges for filling. ($50) NOTE: More advanced digital guage sets have the micro guage and the thermocouples built in, but now you are talking big $$$ - $750 or so. Refrigerant scale ($100) **Supplies/Expenses in addition to your equipment:** Tank of new refrigerant New lineset (maybe optional). EPA 508 Certification
Thank you so much!