Page 1 of 3 123 LastLast
Results 1 to 13 of 37
  1. #1
    Join Date
    Sep 2011
    Location
    Tucson, AZ
    Posts
    14

    Determining the cause of high head pressure

    First I’d like to state that this is not a DIY question. If a procedure is forthcoming in this thread, I’ll have it performed by a professional.

    Specifically I would like to know if there is a procedure to determine if high head pressure is being cause by non-condensables in the system, baring evacuating the system and recharging. The reason why I like to know about this will become apparent in the rest of this post which unfortunately will have to be lengthy to understand the problem.

    The compressor in my Carrier model 38TRA042310 condenser failed after about 16 years of service. I guess that’s not unusual for Tucson, AZ. The solution was to replace the compressor if one could be found. The technician called me later in the day and told me there were none to be had in the local area. The alternative was to replace the entire outdoor unit with a dry R22 unit.

    The repair crew showed up with a Rheem model 13AJA420175. During the installation numerous errors were made; too numerous for this post, but the one that disturbs me the most is that they didn’t use a micron gage during the evacuation of the system. They relied on the manifold gauge which I later found out is old school. The technician didn’t have a scale so he just basically charged the system until it blew cold air. He admitted that he didn’t know how to do this and recommended that I have the charge check by one of their more skilled technicians.

    The more skilled technician found that the system was overcharged and reduced the charge as much as he could. In the end the suction pressure was about 62 psig. The suction line temperature was about 51 degrees. For what it is worth the indoor temperature was about 76 degrees and I would guess the humidity was around 50%. The outdoor temperature was around 85 degrees F.

    What bothered me was the head pressure of 250 psig. According to the chart on the unit, the head pressure should have been around 203 psig. The delta T was around 19 degree F and I was cool again. If I were an average consumer I’d be as happy as a (insert your own simile), but I read enough in books and on the Internet and I’m not happy.

    I realize that it would have been more rational to replace the entire system and upgrade to a 410a system rather than pay $ for this repair on a 16 year old system. Nonetheless when the outdoor temperatures are still above 110 who can be rational? Still I want this repair done right.

    I wrote the manager and told him of my concerns. He finally gave me a call and told me he wanted to consult with the last technician and that he would get back with me. It has been sometime and I think he may be trying to blow me off. I’ll have to call him. Anyway before I talk to him again I’d like to know where I stand.

    He’s is probably not going to offer to evacuate the system and recharge as this is an expensive procedure. I suspect that he will tell me that the high head pressure is due to preexisting restrictions in the rest of my system. So the question remains: Is there way to determine the cause of high head pressure between non-condensables in the system versus some sort of restriction?
    Last edited by beenthere; 09-16-2011 at 07:29 PM. Reason: price

  2. #2
    Join Date
    Feb 2011
    Location
    North East Ohio
    Posts
    774
    First of all, please remove pricing from your post. I would have the "more skilled tech" come back and charge the system by proper procedures. First thing that needs to be checked is airflow. 400 cfm per ton is good in my neighborhood in OHIO. Hopefully someone can chime in about your neck of the woods. Once airflow is verified, I would ask him to recover the refrigerant, pull a good vacuum and weigh in the new charge. It sounds as if the install crew was not prepared for this job and it needs some fine tuning. I'll bet it's still over charged

  3. #3
    Join Date
    Sep 2011
    Location
    Tucson, AZ
    Posts
    14

    Sorry

    I didn't mean to break the rules of this helpful forum. I thought the price in this context would have been ok. Unfortunately I can't see how one can edit ones original post. Let me know how and I'll change it to "a lot of bucks"

  4. #4
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,412
    The chart on the new outdoor unit assumes you have a matched system, you don't! Your old 16 year old unit was most likely a 10 SEER, your new outdoor is a 13 SEER designed to operate with a TXV.

    And yes 400 cfm to 450 cfm per ton works for Arizona.
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,167
    A 13 SEER condenser on a 10 SEER evap can often have a higher then normal head pressure of a matched system. Next, Rheem is design for a minimal amount of refrigerant. Your old carrier coil is not designed for that though. So you got mismatch problem to correct first. Then if it still has a high head, there are ways to determine the cause.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  6. #6
    Join Date
    Nov 2010
    Location
    N. Idaho
    Posts
    586
    As per the AOP Rules only Professional Members * can reply with
    advice
    to the OP. Anyone may post and ask questions. They may even
    question the * member answer but not give advice or expand on the
    advice given. Please read these rules for a complete understanding. AOP Rules
    For those in our industry who wish to become a Professional Member, please click here and follow the
    instructions. Apply for Professional
    Membership
    Last edited by beenthere; 09-17-2011 at 01:44 AM. Reason: No *

  7. #7
    Join Date
    Sep 2011
    Location
    Tucson, AZ
    Posts
    14
    While I don't know the exact figures, the preexisting system had enough air flow and the pressures/temperatures were reasonable. The preexisting system had a SEER of at least 12. The indoor unit was matched to the 3.5 ton outdoor unit. The new outdoor unit is a 3.5 ton unit and the installation manual says nothing about expecting a TXV.

    This probably deserves a new thread about mixing components from different manufactures and whether they can be matched. This thread asks the question: Can one detect if the cause of high head pressure is due to non-condensables in the sytem?

  8. #8
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,714
    Quote Originally Posted by Damien View Post
    Removed Quote
    Damien,

    Please read and follow AOP Forum rules.

    If you have any questions, you can contact an AOP Committee Member for assistance.

    Thank you,

  9. #9
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,714
    Quote Originally Posted by sneuberg View Post
    Can one detect if the cause of high head pressure is due to non-condensables in the sytem?
    Yes.

    It isn't a difficult test to do and any tech worth the name should be able to do it.

    From the readings you've given us, though, I seriously doubt that this is your problem.

    I worked on a Rheem a month or so ago that have VERY similar symptoms and the problem was not non condensibles.

    If the tech/installer pulled even a half decent vacuum measured with a manifold gauge, you won't have issues with non-condensibles. Micron level evacuation is required for the removal of MOISTURE, not non condensibles, really.

  10. #10
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,412
    Quote Originally Posted by sneuberg View Post
    While I don't know the exact figures, the preexisting system had enough air flow and the pressures/temperatures were reasonable. The preexisting system had a SEER of at least 12. The indoor unit was matched to the 3.5 ton outdoor unit. The new outdoor unit is a 3.5 ton unit and the installation manual says nothing about expecting a TXV.

    This probably deserves a new thread about mixing components from different manufactures and whether they can be matched. This thread asks the question: Can one detect if the cause of high head pressure is due to non-condensables in the sytem?
    I'm heading out to dinner, but when I return I'll post an article by Carrier about miss matching!
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  11. #11
    Join Date
    Dec 2002
    Location
    Arizona
    Posts
    4,412
    Quote Originally Posted by sneuberg View Post
    This thread asks the question: Can one detect if the cause of high head pressure is due to non-condensables in the sytem?
    the answer is yes you can.
    Make your expertise uniquely valuable.

    Make your influence uniquely far-reaching.

  12. #12
    Join Date
    Jul 2005
    Posts
    5,572
    If they pulled a vacuum period, and broke the vacuum with R22, then the problem isn't noncondensables. There simply wouldn't be enough air or nitrogen in the system even at 28-29" vacuum to affect the head pressure. The high head pressure is more likely due to an overcharge. Could be other issues on top of that as well.

  13. #13
    Join Date
    Dec 2002
    Location
    SouthEast NC ICW & Piedmont Foothills
    Posts
    7,635
    I'm a little concerned with:
    "The more skilled technician found that the system was overcharged and reduced the charge as much as he could."
    It`s better to be silent and thought the fool; than speak and remove all doubt.

Page 1 of 3 123 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event