question regarding outside unit defrost

[ctscasemod]

Hi,
I have rebuilt an old air conditioner with the external board not working. I have replaced the capillary tube by two txv at evaporator and condenser (this is an heat pump).

The inside unit is working fine, sends the signals to the reversing valve and compressor, thermostat, etc. so i just used some relays to feed the outside unit directly.

The outside board should handle the defrost, that mostly happens with the capillary tube, but since now there is a TXV is there any concern about frost on the "evaporator" (outside)??

Thanks

[Brian_UK]

Short answer - Yes.

Frost builds to ice which blocks coil airflow and crushes pipes.

[Contactor]

The frosting up will occur according to ambient conditions and your evaporating pressure, not what expansion device you use.

If the outdoor board controlled the defrost and is fed by your relays on the indoor unit then I can see why this is causing you a problem.

I'd be interested to see a wiring diagram for the original control circuit and for your mods but wiring the lot from one panel inside sounds like the way to go...

[ctscasemod]

The frosting up will occur according to ambient conditions and your evaporating pressure, not what expansion device you use.

If the outdoor board controlled the defrost and is fed by your relays on the indoor unit then I can see why this is causing you a problem.

I'd be interested to see a wiring diagram for the original control circuit and for your mods but wiring the lot from one panel inside sounds like the way to go...

I haven't tried the unit yet, because the evaporator on the inside unit has an external equalized valve that doesn't have the one way valve to allow reversal of the refrigerant. The outside one has, although it is an internally equalized, so the unit is working only on cooling mode.

The AC has two boards one on the inside unit, with the thermostat an one in the outside unit that reeded the outside temperature and witch one i think did the defrost, so I'm unsure if the internal unit handles the defrost (If yes, what was the function of the outside board!?)
The inside one gives me the signals for the solenoid and compressor directly so i just wired two 24V relays to control them.

I have seen on the web some posts about older units using a defrost timer that worked once 30 minutes or so, I thought i maybe using one. The temperatures in Portugal rarely go below 5ºCelcium.

Thanks, Carlos