Instaling VFD's on package unit

[Raheem]

Hii,

I have 6 package unit Trane brand 20 Tr and it was working just fine, then I install in each one a VFD to control the airflow ( High, Med, Low ) by changing the 2 stage thermostat to Fan coil thermostat Dx.
for the 2 first months, it was working without any issue, but recently all the units state freezing up.

Please support me.

[frank]

Freezing up caused by a lack of heat absorption due to low air flow

[Raheem]

The problem is even with the high-speed VFD (50Hz), the coil still freezing up.

[frank]

Are you talking about the evaporator?
If so, you need to measure your liquid temperature before and after your metering device. You may have set the airflow too high causing excessive sub cooling.

[Peter_1]

If you decrease airflow over an evaporator, you then needs to reduce compressor speed accordingly and maintain an evaporation pressure above the freezing point of water.. It also is possible RH has increased these days