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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8441
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I had a Daikin new series, 4MXS36NMVJU installed. The

Customer Question

I had a Daikin new series, 4MXS36NMVJU installed. The compressor is located outside on the bottom level. the first 2 interior wall evaporators are about 18' away, each, and 8' up the exterior wall. The other 2 units are 26' and 36' away respectively and both about 16' up the exterior wall We pulled vacuum then pressure tested to 150psi 3 times with nitrogen, breaking the pressure with vacuum pump 3 times. We held 900 microns over 15 minutes, verifying sealed and tight, free of leaks and dry enough to charge. twice after turning on the units and testing, all th units blow cold, but after about a few hours, the two units on the 2nd floor stop blowing cold. I don;t believe the code is showing low freon. We thought there might be a tiny leak, so we pressure tested again, checked each joint and it held for hours, so we assumed there is no leak. We turned on the units again and it did the same thing. All units were blowing cold. After a few hours, the upper 2 rooms stopped blowing cold. So we shut off the lower two room units and ran the upper units for 2 hours with no change. Is it the settings, does the compressor need to be adjusted, are we low on freon, are the upper units too far away or too much vertical? HELP!
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.


Tell me what suction and heat pressures you run on each coil... then valve one coil off at a time and tell me what the pressure reads are... until you only have one coil operating.

I need to know the outside air temperature when you do these tests.

So far I suspect a under charge of refrigerant...

Leaks are best detected with liquid (soap bubble) type leak detectors.

My guess is that you do not have any leaks, but just an undercharge of refrigerant.

Let me know about all that, we can go from there.