AC Freezing up at night only...Stumped


Old 07-23-14, 05:56 PM
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AC Freezing up at night only...Stumped

Hey Guys,

Just reaching out for a little help as I'm stumped with what could be causing my AC to freeze up at night. The AC has been working flawlessly for several years up until 2 weeks ago. I have had 3 different technicians come out and check my ac with no resolution to my problem. As stated, my AC freezes up at night only (T-stat set to 77 degrees F), it runs perfectly through out the day. When the AC freezes, both the larger copper pipe and smaller pipe with the dryer brazed in it will be ice cold or have ice on the outside, the outside unit fan remains running even though the compressor has stopped. The AC will not freeze if the thermostat is set to "Fan on" mode. From what I gather, I have a carrier setup which is a piston type. The things we have checked/replaced thus far are as follows:

-R22 pressures checked and are within spec (75/250 I believe, Draw pressure drops to 50 when frozen)
-Thermostat replaced with Honeywell 6500 series
-Contactor replaced
-Duct work checked to ensure no blockage or collapsed ducting
-All capacitors checked and out of spec capacitors have been replaced
-Outside coil and A-frame cleaned
-Blower wheel cleaned
-Air filter replaced
-All electrical connections checked and reterminated when necessary

After all of that, the problem is still present. I am not an HVAC guy but have friends in the industry who have been helpful but have run out of ideas as to what could be causing the trouble. Before replacing more components, I was just looking to see if anyone had any tips on what to check next. Any help would be greatly appreciated.
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Old 07-23-14, 07:43 PM
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Sounds like the filter drier is slightly plugged. If you have frost anywhere on your liquid (smaller) line than you have a restriction somewhere.
Old 07-23-14, 08:07 PM
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Welcome to the forums.

the outside unit fan remains running even though the compressor has stopped.
Are you sure about that ? The compressor and fan should operate together.
Is this a heatpump system ? A make and model would be helpful.
Old 07-23-14, 08:27 PM
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Did anyone check the external static pressure across the furnace?

I once had a similar problem with an ECM motor in a furnace that was running backwards.

Last edited by Houston204; 07-25-14 at 06:23 AM.
Old 07-25-14, 04:47 AM
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Put a pound of refrigerant in it and see what happens.
Old 07-25-14, 02:12 PM
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Thanks for the replies!

I am 100% sure the outside unit fan remains running, the compressor will shut down and all related piping will have solid ice over them with the fan continuing to run. The system is a heat pump system and model off the outside unit is Payne PH10JA060-B.

Today we pulled the A frame again to give it a thorough cleaning, replaced the dryer on the small line, vacuumed and topped off the system. I'm really hoping this solves the issue, but I will see tonight. Any other ideas on what could be going wrong?
Old 07-25-14, 02:46 PM
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Anybody amp. out indoor blower motor? Hard to do and get correct reading with blower door open.My wild guess anyways. Good luck and let us know what you find.

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