temperzone lp faults

[TECH TIM]

hi there guys, hope all is well with ya all, im want to ask if any body may have had some lp issues with temperzone split ducteds,,, i curently have 3 in the one building a rather new building, they are all coming up with low pressure faults, all units run for 5 or so mins and off for 3 or so, all units are running simular pressures and temps, liq line 215psi (1500kpa) and 40 deg cel at outdoor unit suct line was 70 psi (480kpa) and 25 deg cel,,, model of units are OSA126R, these unit hav option for lp switch or bypass,, these ones are bypassed, no lp switch, tech support advised the lp fault would be initiated by suction line sensor?? they also advised to get superheat to approx 4-6k,, ok so i have 70psi indicating 4-6 deg cel in evap on R22, (pressure taken at service valve at outdoor) and i have 25 deg cel on suction line at outdoor unit giving me 19-21k sup ht?? tech suppot wants approx 10deg cel at this pressure,, they suggested short of refrigerant???? i think pressures are a bit high??? i thought around 60 psi suct was good, the ambient of the day these measurements taken was around 26-27 deg, and pipe runs were approx 12-14 meteres, there is absolutly no way in heaven you can get good access to any of the fan coil units its a crazy install if ya ask me but this could be the norm??? take it easy guys dont work too hard;)

[paul_h]

Yep, the sense the suction line temp, not the pressure. The thermistor is normally near the reversing valve.
So if the suction line temp is a bit high, or the thermistor is buggered, you'll get "LP" faults.
You are gettin "LP" faults because, as you said, the suction line is 25C, so superheat is to high.

[wombat]

The suction temperture sensor should be around 10K. I went to the trouble of adjusting the TX on the ISD300Q to find the LP problem did't go away. The sensor was only 1K and didn't show as a sensor fault.

[TECH TIM]

thanks guys, i think i need to play with refrigerant levels, just wanting to ask if yas dont mind, in your experience is there a rough idea on the suction pressure im looking for??? i know 4-6 k super heat is required but i have suction of 70psi (4-6 deg cel coil temp) by adding refrigerant would i not then raise suct pressure and coil temp and make unit useless anyway?? but on the other hand, do i add more to allow more liquid in evap so then it refrigerates down suction line thus allowing me to reduce suction line temp to acheive 4-6 k superheat, im confussed:confused:

[nike123]

thanks guys, i think i need to play with refrigerant levels, just wanting to ask if yas dont mind, in your experience is there a rough idea on the suction pressure im looking for??? i know 4-6 k super heat is required but i have suction of 70psi (4-6 deg cel coil temp) by adding refrigerant would i not then raise suct pressure and coil temp and make unit useless anyway?? but on the other hand, do i add more to allow more liquid in evap so then it refrigerates down suction line thus allowing me to reduce suction line temp to acheive 4-6 k superheat, im confussed:confused:

Do not play with refrigerant levels. Evacuate, evaluate, fix leak if short of refrigerant, then recharge correct amount by weight.

[paul_h]

Best bet is not to play with them and guess or be concerned with pressure. They are not large systems so you are better to reclaim, pressure test, evac and recharge after checking no resctrictions on the piping.
I'm saying that because you have relitively new systems, and if I understand right, all 3 have the same fault?
Possibly bad installation could be the cause then, so I wouldn't be topping up, I'd be starting from scratch.
They could be just undercharged at the time of install, but there could be air in the system, leaks on the joins etc.

[TECH TIM]

thanks paul i was contamplaiting that now im going too do it cheers mate