Iowa Thoughts on Low-Pressure Cut-Out GSHP

Discussion in 'Maintenance and Troubleshooting' started by Cadman, Jan 29, 2019.

  1. Cadman

    Cadman New Member

    Hey Guys, question I'm hoping you can help me with.

    For those following allowing, I installed a Bard 5-ton GV61S1 GSHP in December, open-loop with 6x600' slinkies. Antifreeze is 20% methanol, freezer test shows protection down to 0F.

    I typically run the unit during the day as necessary to heat a large open space to mid-50's/60's and it hasn't been a problem, even with outdoor temps in the single digits. Pressure drop and EWT/LWT's match up against the manual for this config. All humming along nicely.

    Last night the outdoor temp dropped into the negatives so I fired the unit up in advance and ran it all night. it worked great all evening and was working when I went to bed. This morning I found it locked out due to low-pressure. I played around with it this morning and this is what I've found-

    Correct LPS was in-ckt for an antifreeze loop. Room air temp was 38F. Initially, bypassing the switch would not get me any heat, nor cold while compressor ran. Plenty of flow through the loop field as verified in the open loop flow center (15GPM). I put an electric heater at the base of the unit with panel pulled, and my meter on the switch (ckt bypassed). I cycled it back and forth a few times and now I at least get closure for a minute or two before it defaults open. I got the compressor to run long enough on Cooling to get an EWT of 35F and a LWT of 39F and climbing before my meter showed the switch opened, at which point the LWT dropped back down to EWT.

    Thoughts? Does this sound like a refrigerant issue? Could entering air temp be too low?
  2. ChrisJ

    ChrisJ Active Member Forum Leader

    I have read that they don't like starting below 50*F
  3. Cadman

    Cadman New Member

    Well, the room was warmer than usual thanks to solar gain (50's) today but it was still a no-go. I ordered a set of adapters so I can check pressures with my 134a gauge set, should be here Monday.

    Bottom line, set it to heat, and it works for about 30 seconds, then blows cold. LPS (out of ckt) goes open at roughly the same time. Set it to cool, switch closes, cools for 30 seconds, then blows tepid and LPS switch state goes open to match. So it's not just a faulty LPS switch. Loop temp is hanging at 35F through all this.
  4. Cadman

    Cadman New Member

    Well guys, quick update. Ordered up a couple adapters so I could put my 134A gauge set on the unit and determined low side was pulling into vacuum territory. Suspected the expansion valve and sure enough, that's the problem. The capillary tube is snapped clean off! Looks like metal fatigue. Guess it's time for a service call.

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