rooftop charging in winter?

[Nrmika]

any good tips on how to charge a RTU during winter? tried yesterday and set off the freeze stat...

[rundawg]

any good tips on how to charge a RTU during winter? tried yesterday and set off the freeze stat...

Weigh in the charge per nameplate.

[Allen]

Hi Nrmika,
You must weigh the refrigerant charge into the RTU.

Keep warm thoughts.
Good luck,
Allen

[mikeacman]

Yep ,easiest way is to weigh it in ,even if you have to recover the remaining charge (if any )

On a split you can calculate using equipment literature.

Or you can guess,using your tools ,and probably get pretty close, but that only counts in horshoes and hand grenades

[Nrmika]

I was weighing in but it set off the freezestat. Feathering to fast?

[steve wright]

You do have to weigh it in

However you may have to block condenser to keep head up so the suction will stay up so you can get system to take charge without it cycling on freeze stat.

Using cardboard to block entering air to the condenser usually works great

[mikeacman]

To add ,I use my recovery machine to recharge units . I can weigh it all in before I even start the unit up....

After all ,its a refrigerant pump....

[meplumber]

To add ,I use my recovery machine to recharge units . I can weigh it all in before I even start the unit up....

After all ,its a refrigerant pump....

Mike is right. That is how we do it in cold weather. Awful hard to create enough head even with blankets and cardboard when it is below zero. Which means that we wouldn't be able to work on them all winter. So we put the weighed charge in with the recovery machine, then start it up. Never fails, we always have to go back in the summer and trim the charge or adjust the TXV, but it gets us close. Sucks doing AC work when it is below zero.

[steve wright]

Wow down here 20f is cold

I say let's drink some coffee and charge it next summer

That trick is a first for me I sure hope I never have to use it

[hands]

If the system was evacuated to 500 microns or lower, You should be able to get most of the charge in without even starting the unit. I will use a torch to warm the refrigerant drum if it won't pull in the entire charge by itself. You could also use a heat gun if you have one, but a MAP gas torch works great.

[mikeacman]

If the system was evacuated to 500 microns or lower, You should be able to get most of the charge in without even starting the unit. I will use a torch to warm the refrigerant drum if it won't pull in the entire charge by itself. You could also use a heat gun if you have one, but a MAP gas torch works great.

that works...

A lot of the places I service would politely escort you of site and never allow you to return if caught putting a flame to a pressure vessel ....

[BaldLoonie]

Sell them an economizer?

[hands]

that works...

A lot of the places I service would politely escort you of site and never allow you to return if caught putting a flame to a pressure vessel ....

They would probably do the same if you were caught with a control panel open and you didn't have your PPE gear on, but that never happens either does it.

[rcac101]

Take a large plastic garbage bag and wrap it around the condenser. I usually let the fan hold it in place and charge the system its quick and easy.

[mikeacman]

They would probably do the same if you were caught with a control panel open and you didn't have your PPE gear on, but that never happens either does it.

you are correct

[meplumber]

Take a large plastic garbage bag and wrap it around the condenser. I usually let the fan hold it in place and charge the system its quick and easy.

Hard to find a big enough garbage bag for a Rooftop Unit. That trick works until it gets really cold.

[steve wright]

.....back in the day with r12 we had heaters(electric) that went on a 30# drum and Robinair (are they still in business) had a charging cylinder that had a heater in it.

But all that is a little over the top!

[54885488]

Carefully cycle outdoor fan motor by hand ?

[2sac]

5 gal bucket with hot water. 30 lb jug fits right in there.

[steve wright]

He has to weigh the charge in.

But I will use that cardboard to block the condenser