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Yes that initial 100psi pressure at 80F shows you still have full system charge. Mine is 110psi at 90F because I live in the tropics. And my charge weight was 950gm.
If you refer to Smart VOV install guide (I guess you're using this as this is the most commonly available VOV in the market) it is recommended to charge 90% of the usual R12 charge weight. Old charge weight for 740/940 using R12 is 1100gm. So that means 990gm for the R134a charge. What I'm getting at is that to use VOV you may charge a little bit more than the standard weight because VOV fitted AC tend to run at very low suction pressure (and this overcharging is to compensate for that). This very low suction pressure is what makes the AC very cold.
See smart VOV install guide:
http://www.aircondition.com/vov/install.htm
After seeing your AC pressures it seems now you have few choices:
1. Add more R134a (another 40gm) so that the low side pressure is able to stay above 29psi and not trigger the low pressostat to OFF the compressor. This recent incident of rapid cycling may be due to normal refrigerant loss over the years. In short top up the AC a little bit more. If rapid compressor cycling STILL happens after topping up then it is CONFIRMED that you have an intermittently stuck VOV.
2. Install a new VOV. This if you really need the performance gain that VOV provides.
3. Put back standard OT.
Regarding your low pressostat not triggering OFF the compressor at below 29psi, leave that be for the time being. As you've said your gauges may be a little bit inaccurate.
My VOV did something more last time. There was occasional "farting-like" noise when the compressor kicked-in. I guess there might be some local turbulence during the initial refrigerant flow. It was these intermittent issues that had me decided to put back the standard OT albeit some performance loss.
Hope these help,
Amarin.
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