30 gtn chiller

[Milliamp]

i have a 30 gtn carrier chiller going out on low evap pressure code a133 i have guages hooked up to the compressor and when it tripped out with this code my pressures where high enough past the 90 second time for the control board to trip. The onley other thing was i noticed the low pressure switch not always opening so i changed switch and ran all day long no problem . But maybee what else could it be because it seems to trip at night when lower ambients.thank you on this.

[txhvac]

Post a log of the chiller, lots of things can cause low evap temps, Sensors in the compressor & in the evap need to be checked, Exv operations, charge, waterflow etc.

[Milliamp]

It is going out on low evap pressure a133 temps in and out of evap ok now sensers on compressor just sensers on ent and leaving water and sat cond temp senser.i have a four pound water drop across evap sensers reading close to temp guages . And when it tripped i had like a 70 pound suction pressure .

[Dallas Duster]

Model number please must be a single compressor unit? If so what kind of head pressure controls do you have?

[Milliamp]

Yes it is a single compressor unit has two fans a saturated cond temp senser and i believe this senser also controls the one fan. IT also has a hot gas bypass but When i saw it tripp my guages on suction say lik 63 to 70 pounds of back pressure.in the book it says low pressure switch faulty expansion valve low charge etc. But my guage pressure is ok on suction side so it does not seem mechanical . So i fixed connecter on board for low pressure switch and added adjustable low pressure control and it ran good all day long. The only thing is what could be causing this to happen at night thank you reply if you like.

[Dallas Duster]

What kind of night time temps are you having and what is controlling your first fan pressure switch of anykind or is it coming on with the compressor?

[Milliamp]

The night temps are between 38 and 50 degrees the last couple of days but the second fan i believe is controlled on pressure control and never comes on during the day while i was there because it does not need to the first fan is running full blast with no fan control with the compressor but we had this chiller for a while and this is the first time we noticed this problem.

[Dallas Duster]

Like others have said check and verify your flow and make sure your flow switch is working properly. The you might want to force your #2 fan on and see what happens.

[Milliamp]

Ye I have 10 psi going into barrel and 6 going out of barrel 4 psi drop across evap. And the temps on the water are close compared to the sensers and the water loop is a close loop

[txhvac]

What size is the machine? 9.24 ft of head a little on the low side, but still acceptable. What kind of valves are on the air-handlers? You say you fixed a connection on the micro? This kept the circuit on all day & tripped @ night or morning? Is your charge good? Suction pressure only tells people so much if you can't produce water temps, head pressure, superheat, subcool etc. This turns into speculation, it could be this or it could be that, nothing real solid. Do you have motormaster controls? Food for thought.

[Milliamp]

Yes sir I understand I just fixed connection on control board for low pressure switch because my meter leads across switch while running showed 24 volts like the switch never close while running and I installed new mechanical switch and set my adjustments on it for cut in and cut out.it ran great all day yesterday while troubleshooting after o installed new switch just wanted to pick peoples brain on this thanks reply the model #is 30gtn020de500 thanks