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  1. #1
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    Ptac freezing coil

    Working on an Amana PTAC model # PTH153E35AXXXAA SN: 1003601937
    The evap was freezing up frosting up all the way to the compressor. I suspected low charge so I pulled the charge and found it only 2 oz. shy of factory specified charge. I brazed in high and low side accesses and recharged to factory charge of 36.6 oz. 410A. No change in freezing of coil. I'm reading about 70 psi suction and 320 psi liquid. 7.7 degrees superheat and 14.3 degrees subcooling. I'm thinking I have a cap tube issue, but not sure. I haven't seen this before on one of these units. It is only a few years old and never had any major service done on it. Any suggestions or ideas would be greatly appreciated.

    thanks

  2. #2
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    Sep 2018
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    Florida
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    Yes I have a suggestion for you: Clean blower housing and replace the blower motor.

    So you have an airflow issue, or compressor issue.

    On a PTAC the best you can do is clean that off, and honestly for 410a you want to see somewhere around 120 suction and 320+ discharge at ~70-80 Indoor temperature.

    What is the rated amp draw of these: blower motor, compressor, OD motor(condenser motor).
    And finally, what is the actual amp draw of these parts?
    Last edited by Goldwaves; 09-04-2019 at 02:48 PM. Reason: Remove goofiness.

  3. #3
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    Mar 2019
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    Thread Starter
    Blower housing is spotless, and coil is clean. Blower RLA-0.27 actual-0.21 compressor RLA-6.2 actual-4.5, condenser fan RLA-0.48 actual-0.42

  4. #4
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    Aug 2002
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    Southold, NY
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    Visually clean or did you wash them out?

  5. #5
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    Mar 2019
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    Thread Starter
    I washed them with triple D

  6. #6
    Join Date
    Sep 2018
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    Florida
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    Did you also clean the filter? What's the voltage going to the unit (check outlet voltage, then load voltage)

    What type of metering device do you see? That and the capacitor isn't listed.

    Seems like electrically it's good
    Mechanically good- possibly
    Chemically: nope.

    I would adjust charge based on SLT and amp draw at this point. Get it right above freezing. I hope you changed that drier when you pulled the charge.

    Actually one more thing, did you put the system under a vacuum before adding refrigerant?

    That unit might have a small leak. If you don't find one and adding refrigerant fixes the issue then schedule for a new unit anyway. That thing is like 900 bucks, could've installed a new one by now.

    Best of luck to you.
    Last edited by Goldwaves; 09-04-2019 at 04:24 PM. Reason: More to do

  7. #7
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    Mar 2019
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    Thread Starter
    voltage is 208. Need to check load voltage. Metering device is a cap tube. I used 2 braze on piercing valves and after pulling the charge I pressurized with nitro it held 250 for around 2 hours. I didn’t change change the filter dryer, but pulled 500 microns on it before charging. I work at a large resort in the Poconos, so I tinker with these kind of things when I’m not putting fires out. If I don’t figure it out I’ll just send it to the scrap dumpster. I’ve only been doing HVAC & refrigeration for a few years so I like to figure out theses oddball problems use them as learning experiences if nothing else.

  8. #8
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    Mar 2019
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    Thread Starter
    Also I’ve already replaced the unit. It’s currently in my shop on the bench

  9. #9
    Join Date
    Jun 2019
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    So Cal
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    How long does it take to freeze the coil? Is it after hours of running or almost instantly? Is the condensation water draining properly?

    I have worked with literally hundreds of PTACs specifically Amana. Most of the time our coils were freezing was due to condensation water sitting in the pan and not draining which would get picked up by the blower in to the coil and then slowly freeze over.

    Check that the drain switch is working as well and lastly replace the SA sensor as a way to eliminate the possibility of it running past desired SP.

  10. #10
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    Sep 2018
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    Florida
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    Quote Originally Posted by Clifford21186 View Post
    voltage is 208. Need to check load voltage. Metering device is a cap tube. I used 2 braze on piercing valves and after pulling the charge I pressurized with nitro it held 250 for around 2 hours. I didnt change change the filter dryer, but pulled 500 microns on it before charging. I work at a large resort in the Poconos, so I tinker with these kind of things when Im not putting fires out. If I dont figure it out Ill just send it to the scrap dumpster. Ive only been doing HVAC & refrigeration for a few years so I like to figure out theses oddball problems use them as learning experiences if nothing else.
    A 2hr pressure test, good lord I hope that sandwich was tasty.
    Yeah well you see here, there is a chance that there was/is restriction that capillary tube.
    This is how that should have gone down to begin with:
    See unit evaporator icing up.
    Defrost unit and check for leak.
    No leak found- hook up gauges check pressures and temperatures. A good time to check amp draw and what have you as well.

    This unit is more than likely leaking, and more than likely at that cap tube nut-
    Fix the leak, pressure check with nitrogen, or "seal and fill". Restart unit...

    Observed suction pressure still low after the leak fix - bad compressor.

  11. #11
    Join Date
    Sep 2019
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    Ptac freezing up

    did you add refrigerant to compensate for lineset

  12. #12
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    Mar 2019
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    Northeast PA
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    Thread Starter
    It starts freezing the coil within minutes and freezes to the compressor within 10. I’m starting to think it’s a compressor issue but wouldn’t my high side pressure be more out of wack. 320 psi in a 72ish degree shop isn’t too far off the mark. I’m positive it’s not a leak. Immediately after charging to factory specs and running coil started freezing. It starts at the cap tube outlet and within 5 min the coil is frosted over. I’ll pull & weigh the charge in the AM just for shits and giggles.

  13. #13
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    Mar 2019
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    Northeast PA
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    Thread Starter
    No condensate in pan during initial start up. Drain valve bent up to not impede drainage

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