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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a 14 seer aireflo / lennox 3.5 ton 410 heatpump

Customer Question

I have a 14 seer aireflo / lennox 3.5 ton 410 heatpump system. System is charged good on ac in cooling mode but when turned over to heat it sky rocket head pressure shooting it over 600psi
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, it is easy to charge a heat pump in cooling mode with a little too much refrigerant so that the head pressure goes high in heating mode.

There are other factors than that however, if air flow across the indoor coil is a bit lower than specifications due to a dirty air filter, or more commonly air duct sizes a bit undersized, the system will adapt to that in cooling mode by adding a little extra refrigerant, but in heating mode that lack of air flow, and extra refrigerant runs the head pressure up beyond viable limits.

I suspect that is that case here, although you should know, that in my 51 years I have yet to meet an HVAC contractor who skimps on duct size who will admit to it... An air balance test is required to sort this out if you need proof.

However if you can tell me the duct sizes and how long each run of duct is I can get pretty close with calculations.

If you appreciate my input so far, locate the "rate your expert" link, and rate my work positively... we can go from there.

Lacking that I can spend days with a customer at my own expense,without any compensation. Rating does not increase your charges or close the question and it allows you unlimited follow up... in this case for air flow calculations or advice on how to deal with the contractor or his staff who often to do realize the ramifications of undersized air ducts in a heat pump system.