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  1. #1

    Hot in the afternoons in Texas

    My air conditioner typically runs fine, but recently about a week ago in the mid afternoon it shuts off and I have to go out and push the reset button on the back panel of the outside unit. It starts up and runs properly for about 20 hours or so, then shuts off.

    I had my normal ac man come out and check everything. I had cleaned the coil and replaced the contactor, earlier. Anyway, he says the unit is working fine and gave it a clean bill of health, only that it was an older unit of 12 years old. It had full coolant, fan motor runs fine in both the outside unit and upstairs. The only thing he said that was slightly high was it was pulling 22 amps and not 20, but that was normal for the 105-6 degree days we are having in Texas. 2 -3 hours later it turned off again, I turned off the thermostat, pulled the breaker and put it back in, reset the reset button, turned back on the thermostat, 5 minutes later it starts up and continues to work fine.

    Do you have a possible suggestion?

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    When you say the coil was cleaned, do you mean the outdoor coil? And if so, did your tech verify if the coil had two rows?

    If you have a condensing unit with two rows of coils, and those rows are not split to clean between them, your unit could still run high head pressure even if the outer row of coils appears clean, and even if you or your tech cleaned them without splitting the two rows. Reason? Dirt becomes trapped between the two rows and cannot be dislodged with a normal water or even water/coil cleaner flush.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  3. #3
    Join Date
    Jun 2012
    Location
    East tx
    Posts
    164
    That "reset" button is a high pressure switch. Either your coil was not cleaned properly(highly likely) or you have a restriction in refrigerant circuit that is still tripping on the high pressure switch..if both turn out not to be the case and the freon is fine, i'd suggest replacement of the high pressure switch. If it's a rheem/rudd unit it probably can't be disconnected so another one will need to be added.

  4. #4

    Crazecodyk

    Thanks for the reply.

    Yes, it is a Rheem. So it either needs a HP switch added & or clean the coil better? Thank you.

  5. #5
    I think there is only one layer of coil on the outside unit. The inside had been cleaned just a few weeks ago and rechecked yesterday.

  6. #6
    Join Date
    May 2008
    Location
    Myrtle Creek. Oregon
    Posts
    182
    it is possible the unit could be over charged just a tad. that and hi ambiant temp. plus a dirty cond. all this could cause hi cond. pressure. somthing to look for.
    a stupid question is a question you wont to ask, but don't

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    Quote Originally Posted by cboe View Post
    it is possible the unit could be over charged just a tad. that and hi ambiant temp. plus a dirty cond. all this could cause hi cond. pressure. somthing to look for.
    Plus one. The tech should check superheat and subcooling when he checks refrigerant charge. An overcharged unit will have skewed readings, even under high ambient conditions.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  8. #8
    Join Date
    May 2002
    Location
    Houston Texas
    Posts
    6,327
    There are many reasons for the unit to be tripping the HP switch including all of those mentioned.

    It sounds like there could be an intermittent problem with the fan motor or its capacitor. Rheem units have a high failure rate of condenser fan motors and capacitors, frequently the incorrect motor is installed which will improperly place the fan blade. Rheem units also have a big problem with oxidation of the condenser coil causing high head pressure.

    Look at the coils (condenser) and see if the fins are turning white and flaky.

    It could also be a problem with the TXV.

  9. #9
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031
    Do you have cottonwood trees in your area?
    It can be difficult to wash it out of the fins.

    The compressor discharge temperature should be checked & should not be much above 225-F. Some units have a temp-limit reset on the compressor discharge pipe.

    Make absolutely certain there is NO hot attic or garage air being drawn into the Return Air; in the mid-afternoon until 7 or 8-PM that could also trip the high pressure switch or the discharge-line temp-switch.

    As stated above; the Tech should always check both Superheat & Subcooling plus indoor CFM air flow, for the optimal airflow for the indoor conditions.

  10. #10
    Join Date
    Nov 2004
    Location
    Austin, TX
    Posts
    888
    Your problem is typically caused by.

    1. Poor outdoor airflow caused by:
    1a. Dirty outdoor coil or dirty inner layer of outdoor coil.
    1b. Worn condenser fan motor. It's slowly overheating and eventually shuts off on internal overload. The overload cools off and the motor will work again once the high pressure switch is reset. It may take an hour to overheat. Had one doing this two days ago.

    2. Defective high pressure switch. They do fail occasionally. I've replaced one or two in 8 years.

    Isolating the slow failing part takes time, time that some technicians aren't used to taking. (many companies allow a limited diagnostic time per call)

    Based on experience I'd replace the condenser fan motor if operating refrigerant high side pressure wasn't excessively high after 10 minutes of operation. I've seen older motors work fine for a while and slowly overheat. The motor shuts down on internal overload. The system isn't able to get rid of the heat it's bringing from the indoors. The heat causes the pressures to climb then the high pressure cut out switch shuts everything off.

    A dirty coil typically causes the pressures to be high and the small refrigerant line that goes into the house to be very hot almost from the beginning. Pressures will climb within a few minutes of operation and the liquid line (smaller line) is very hot. ( it's normally 4-12 degress above outdoor temp. Much more above that can indicate a problem)

    A worn condenser fan motor may have high power usage or the power usage will start out normal and begin to climb slowly as it operates. If the fan motor power use fluxuates slightly during prolonged monitoring and slowling bumps it's way up then it is highly likely the motor is worn given the run capacitor was already checked out. A brocure could be written on diagnosing electric motor wear.
    We always include the run capacitor as part of a motor replacement to prevent a callback if the the old cap were to fail within the next few weeks.

    Sometimes it takes a while to make a correct diagnosis and the customer isn't always well served by speed.
    I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.
    ― Benjamin Franklin

  11. #11
    Thank you. Last 2 days have seen no problem. However I turned off the system for about 30 minutes in the morning each day. Not certain that has done anything. But it runs the rest of the day.

  12. #12
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,915
    My money would be on worn bearings in the condenser fan motor.
    If more government is the answer, then it's a really stupid question.

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