×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

How to optimize R410a charge in HP in cold weather?

How to optimize R410a charge in HP in cold weather?

How to optimize R410a charge in HP in cold weather?

(OP)
I know that the optimum method of charging a HVAC system is to evacuate and weigh in the refrigerant.  Then check the superheat to be around 10F in cooling mode. (No.. I frequently do NOT have the manufacturer's chart for the equipment I have to service!)

My second best way is to install a sight glass in the liquid line at the inside coil and charge until the bubbles go away plus maybe a  half pound. Again in cooling mode. This works fine except a) in cases with a lift of more than one story or b) where the attic area where the inside coil is located is above about 80F when you charge.  I also double check by calculating the superheat. (Why do I install a sight glass at all?  Because, in case a leak starts, it allows the customer to check  bubbles in the liquid line and call for service BEFORE his house gets to the uncomfortable stage.)

These work well for me as long as the OAT is above about 50F allowing me to run in air conditioning mode.

But in frigid weather, I still have situations where I have to pump down, repair a leak and recharge a heat pump. It is simply too costly to "start from scratch" and weigh in the refrigerant unless the unit has lost the whole charge.   The method I use is to set the "actual suction pressure" at the third access port on the HP to something in the range of 100 to 125psi (for R410A) and then go back on a warm day and check it.  Usually this is fairly close, but never precise.

Is there some pressure/temp measurement procedure that you engineering folks know about that will get me "on the money" when the OAT is freezing and below?  Everything I have tried seems to be off more than the 100>125psi "guestimate" I use.  SURELY there is an accurate way.

PS> Most systems I work on have a TXV on the inside coil and a piston orifice on the outside coil.  On the few systems I see with a TXV on both ends, I have no problems.

Thanks.
Joe M
 

RE: How to optimize R410a charge in HP in cold weather?

(OP)
PING!  Surely one of you Mechanical Engineering folk have a better answer to this question!??  Thanks.

RE: How to optimize R410a charge in HP in cold weather?

Why not weigh in the charge, as you mentioned?  And account for the liquid line length in the weight.  Why is it so costly to weigh the gas?
 

RE: How to optimize R410a charge in HP in cold weather?

(OP)
Weighing the R410a works well.  But all up it takes me about an hour to do the removal, compute the right charge and weigh it back in.  I am hoping that there is a faster way.  But maybe not.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources