low pressure control

[prestiege]

had a call on a R12 walk in cooler today,only second time working on a walk in, coil was frozen due to clogged evaporator, pressures at 10 suction 140 discharge, low pressure control set at 32 cut in 20 cut out but unit is still running, closed off disharge valve at compressor and got to 5 psi on suction and still running, cooler set to defrost from 2 am to 5 am, added 3 more defrost settings changed for 30 min shutoff, midnight 6am noon and 6 pm, cleaned evap and condensore coils and replaced LPC,

noticed no pumpdown solenoid or tstat,sold to costumer for next week installation(recovery machine in the shop)

the new LPC i put in still doesnt shut down the unit, from factory it was set to 45 cut in and 20 cut out, after installed unit turned on at correct pressure system was equalized at 34 when i chanded cut in to 32 unit started running, but now it still doesnt shut off at the cutout setting, i need to fix this before the pumpdown is installed or its not gonna do any good, whats the chances of a bad LPC new out of the box, and or what can cause this thing not to cut out right now its set to 32in 14 out and evap is frosting evenly and suction gets to 12psi and unit wont shut down

[Milk man]

Sounds like evap could have iced due to the fact that it never shuts off. Check the wiring or contactor may be sticking closed.

Can you pump down the system using the king valve on the reciever? This will allow you to add a solenoid without having to recover the charge. Wire the stat to control the LLS and the LPS to control the condensing unit's contactor.

[Edited by lynn rodenmayer on 08-19-2004 at 08:38 PM]

[orland25]

helo friend; you sure the you prove the LPC, with the gauges and freon tank only. to be sure has the correct setting. ONLY= GAUGE- HOSE- LPC- FREON

[prestiege]

i can pump down using the king valve, thats how i tried to test the LPC and it never shut the unit down, i didnt have a tank of any refrigerant with to test the LPC as orland25 sugested. why no tank, long story,im working out of a car for time being. but evap clean now defrost timer adjusted with 4 30 min cycles, but new LPC still wont shut the unit down on a pressure drop,all wiring is kosher,120v system disconnect to timer,timer through LPC to compressor. im leaving tonight for a lil vacation, ill check the old LPC with my gages and freon tank upon return, but i pumped unit with king valve to 5 psi with control to cut out set to 20 and unit was still running so even if i add the LLS and tstat at this point it wont do any good till i can get to the bottom of the LPC

just noticed i posted in wrong thread, sorry, feel free to move if nessesary

[bigjohnohvac]

Check wiring maybe not opening contactor coil doing something else??? Check voltage on coil to delivery voltage could be miss matched. Don't know voltage but what if it was 110 VAC and the LPS switched the neutral and the contactor had ground tied to it thus maintainig power all the time???
Line on suction side of system, or could it be on the pressure side ?????