View Full Version : Question....Lennox

16-09-2017, 06:08 PM
Hey all,

Retired for some years now....410a heatpump split which I am now familiar with somewhat thanks to the manual. Anyway a quick question on a Lennox 2.5 ton unit of one of my neighbors. I've been trying to monitor this for as much info as possible. The lockout goes active after 5 low pressure incidents. Pressures look good. They leave for the summer to go up north leaving the AC on about 80. I check out side and the can tell the units been running. Okay so, new house, they already replaced the evap and DC fan on this thing? (I fail to see any savings here from efficiency). I replaced the board, relatively cheap. Talked to one of the techs that serviced this thing and he never got back to me. Okay so here's the problem. Unit goes into low pressure lockout however, all summer being it's left on cooling it's fine....that's what I know up to this point. I suspect the change over from heat back to cool has something to do with it. Just wondering if the reversing valve somehow could cause this? I can never catch a low pressure situation, the unit may operate for weeks or a month before this happens in the winter. In Florida we use heat but can quickly need cooling some warmer days in winter. Any thoughts?

16-09-2017, 06:38 PM
Low side on heating mode should read between 130 to 150 psi.

Fan speed should control the pressure, I would check it.
4 way valve sound OK as if it had any problem, low side reading would be very high.

The Viking
16-09-2017, 08:55 PM
Without knowing the details about that specific unit, I would look at items the system use differently in heating compared to cooling.
- Are there different expansion devices?
- Different non return valves?
- Driers?

Then, is the system short of charge?

If all else fails, try to run it in heating and see where the pipes get cold... Most likely this will point you to the blockage.

Happy hunting.