Issue with high head pressure on Lennox unit
Comments
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Sounds like a head scratcher.
Does it have the correct condenser fan motor and blade with the right RPMs and the correct rotation?
Is the blade mounted at the correct height?
It's possible the condenser fins are no longer bonded to the tubing and not rejecting heat.
Is the liquid line leaving the condenser ripping hot or cool. Check the subcooling and superheat. They will probably point you in the right direction.
If you spray water on the condenser does it run with normal pressures?
Was it evacuated properly? Sounds like non condensebles
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Sounds like the TXV (or EEV?) shuts down. Does the vapor side drop as the liquid line rises? The bulb is in the right spot?0
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Did it ever work correctly?0
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Super heat and Sub Cooling Readings?
Does that have a split condenser coil?0 -
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We recently had a similar issue on four newly installed units. Turns out, because the the building is empty with no load, when it goes into de-hum, it trips compressors on high pressure. The installers removed De-hum wire from tstats and problem went away. We'll re-connect when people return.
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Did it ever work right?
The fact that your low side pressure remains the same indicates that the problem is not there or in the TXV; it's in the high side.
I had a Comfortmaker back 25+ years ago that another tech had miss-diagnosed with a bad reversing valve that was only a couple of years old. He put in a new unit and I took that one and replaced the reversing valve and installed it in my house. It tuned out that when I fired it off the compressor was a no-pumper. I got a new one under warranty and installed it. When I fired it up, the head pressure went crazy like yours. Long story short, it turned out that two passes of the three pass parallel condenser coil were piped dead ended together from the factory rendering them useless and leaving only one pass working.
If you've done all the obvious things right to correct the situation, look for something unusual.Bob Boan
You can choose to do what you want, but you cannot choose the consequences.0 -
Ironman said:
Did it ever work right?
The fact that your low side pressure remains the same indicates that the problem is not there or in the TXV; it's in the high side.
I had a Comfortmaker back 25+ years ago that another tech had miss-diagnosed with a bad reversing valve that was only a couple of years old. He put in a new unit and I took that one and replaced the reversing valve and installed it in my house. It tuned out that when I fired it off the compressor was a no-pumper. I got a new one under warranty and installed it. When I fired it up, the head pressure went crazy like yours. Long story short, it turned out that two passes of the three pass parallel condenser coil were piped dead ended together from the factory rendering them useless and leaving only one pass working.
If you've done all the obvious things right to correct the situation, look for something unusual.
It also sounds like the TXV isn't being starved, so doesn't that leave only one possibility, not getting rid of heat?
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment1 -
Harvey Ramer said:If you have a nested (multilayered) condensor coil, you may have to split it to get it cleaned properly.1
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EBEBRATT-Ed said:You can't diagnose anything without superheat and subcooling readings.1
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