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So after  replacing some cheap  hvac circuit boards,  twice,  and seeing the price go astronomical  I am  retrofitting  my Heat Pump/AC and Air handler with a micro plc,   AB  820,  a 3 phase blower motor, and a VFD.  Now I have a basic idea of how the system operates,  I can write a program using a PID block to control my fan speed,  etc.   As far as I know,   the compressor   starts and runs when heating and cooling is called for.  I am not sure if there is a pressure switch for the fluid to control that on/off   and pressure cut out safety switches to protect the compressor etc.    If any1  has knowledge of  HVAC operation,     and you have time to do a short write up for me so I can program,  plz do so. 

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On 3/30/2022 at 4:35 PM, Wittmann said:

So after  replacing some cheap  hvac circuit boards,  twice,  and seeing the price go astronomical  I am  retrofitting  my Heat Pump/AC and Air handler with a micro plc,   AB  820,  a 3 phase blower motor, and a VFD.  Now I have a basic idea of how the system operates,  I can write a program using a PID block to control my fan speed,  etc.   As far as I know,   the compressor   starts and runs when heating and cooling is called for.  I am not sure if there is a pressure switch for the fluid to control that on/off   and pressure cut out safety switches to protect the compressor etc.    If any1  has knowledge of  HVAC operation,     and you have time to do a short write up for me so I can program,  plz do so. 

I used to know this stuff thirty years ago ! Not really up to speed right now.

S!

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  • 1 month later...

A good start.  Some wiring and cleanup to finish.  Right now. I will be using 4 or 5 contact inputs to vfd for some preset speeds. When i get my dp transmitters. and thermistors I will switch the vfd speed over to pid control using modbus. This will free up. Some relay outs which i will then use to replace my sprinkler system controller

20220509_221817.jpg

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