Hi all, needing some advice. We have been asked to look at a swimming pool heat pump which is under warranty. it has worked well for the past 5 months but has recently started icing up on the evaporator. The heat pump is located within the pool building (around 18c today) and expels its air through a short duct to the outside.
Refrigerant is R410a, suction pressure around 6 bar, high side around 18 bar. Suspected system was short of gas, recovered and weighed it, not short, recharged it. When running the system the whole evap begins to frost, which is no surprise I suppose as its evaporating below zero but we were unable to get the pressure up.
We spoke to an engineer who does work for the supplier who said they had had some bother with incorrectly set expansion valves, after adjusting the valve there was still little difference to evap pressure. Exposed the valve bulb and heated it and the valve clearly modulates.

Any ideas guys?

Thanks