Not performing!

[Wibbs]

Hi all.. Looking for some help and advice with the following.. Maybe someone has come across this before.

We recently picked up a new customer. Over the last couple of weeks we have found out that a number of different engineers have worked on this unit but each time they manage to achieve -18'c it only lasts for a short time then it's back to an engineer looking at it again.

To try and keep it short..

It's a 1x cond and 2x evap system running on R404A. The compressor serial states 1993, not sure if it's been re-manufactured since new. I'll find out the compressor details as I don't have them to hand this morning.

Unsure of the evaps as the serial plates are heavily worn so we are unable to find out whether the system is correctly designed - I'm working with one of the popular suppliers to hopefully figure that out.

A bit of history..

One of the evap (Evap 2) had defrosting issues, they had replaced heater bars and a number of fans. Once the heaters failed again, a new engineer quoted an obscene amount of money to replace them so the customer said no. This decision must have been made easier with the engineer saying he could just remove that evap from the circuit. So he disconnected the liquid line solenoid valve. He then changed the working evap expansion valve from a T2 to a T5. The liquid line goes from 1/2" at the receiver through the drier and s/g, it then opens up to 5/8" until the coldroom. As it breaches the room it is reduced again to 1/2 and then 3/8 through the sol valve before jumping back to 5/8" as it enters the evap body area. Suction line remains the same 1 3/8".

This liquid line had a kink in the 3/8" section so we've removed all that and replaced with 1/2" line and sol valve. We also re-introduced Evap 2 into the circuit. We correctly wired the heaters and removed all the U/S heater bars, leaving the few remaining heaters. Our price to supply new heaters was accepted so we fitted them. We also changed the orifice (which was heavily clogged) as well as the T2 exp valve. We've positioned and insulated the sensing bulbs correctly. New 304 drier to replace the previous 164. It's also had its refrigerant replaced, pressure tested, triple vac'd - the works.

When it was running only on Evap 1 (T5 valve) the suction pressure was approx. 23psi at room temp -5'c. Discharge was 275psi but builds up over time if the unit is constantly monitored. Sub cooling has been 10/11'c but due to excessive head pressure when we recharged unit we stopped at 275psi (7'c SC) compressor superheat is extremely high at 33'c.

Suction Line temp: 10'c
Sat temp: -23'c (23psi)

Liquid line temp: 37'c
Sat temp: 44'c (275psi)

My next move is to put Evap 1 back to how it was with the T2 evap. My thoughts were that the evaps need to equally split the duty and this has been confirmed by the tech guys at our supplier.

Summary:
Running Evap 1 on its own is higher than normal head pressure.
Running Evap 2 on its own is normal head pressure but low suction (and we find the pressures are fluctuating a lot. Suction 8psi - 19psi discharge 200psi - 250psi. It fluctuates quite quickly and can been seen happening. The sight glass also changes from full to bubbles when the fluctuation is taking place.

Running both evaps have approx. slightly better suction and higher head pressure.

The best performance that has been achieved is -14'c but that is only achieved by adding more refrigerant but the head pressure is then over 320psi. Ambient temp is 22'c, condenser has also been washed.

Sorry for the big story. Hopefully what I've listed paints a picture, if more details are required let me know and I'll put them on once I've consulted my notes. I'll also post the comp details later as well as continue to try and get the unit details on the evaps. They are old, 3 fan searle units (black fans).

[al]

Check evap two fans are running and blades/baffles are correct/fitted.
evap fins clear and not crushed internally preventing air flow?
liquid line teed equally to both evaps, maybe fit temporary sight glass on both evap to check liquid at valves?
Correct sizing would be first item to confirm though as you say/

[cadwaladr]

Have you cleaned the condenser 100 percent what's the air on and off the condenser?

[Wibbs]

Thanks for the replies guys. Figured it all out now that I've got all the correct history and unit information. From now on I won't believe anything I hear from the customer as it was all mis-leading. The cold room had another system installed but the comp has gone on that. They've insisted the room was @ -18'c. It wasn't how it currently is anyway...

This unit/system has been installed incorrectly from the very beginning. The 2x Searle LC units are nominal 14KW each. So that means that the condensing unit is only suited to one evap. The previous engineer isolated one evap by de-energising the solenoid valve. If he/she/them found out the unit capacity they would have removed it completely from the circuit which is what we intend to do first thing on Monday. Once she gets a solid flow of liquid we'll see what she puts out. The one evap running has a TES5 with No.3 orifice which is correct so hopefully just a bit of tidying up the pipe work and it should be all good.

I was surprised to hear the evaps were manufactured in 1989 and the condensing unit was 1993. That's some old kit. I doubt I can convince the customer for a new kit install though. That said I'm not sure this system alone will cope. Waiting on spec for new system from a supplier.

Cad.. Yes mate, condenser washed out correctly.

Thanks again...

[cadwaladr]

Had a call to a customer last week. Fruit and veg chilled room not cooling found a major leak repaired it vacced and recharged 134a,quite a large room 10 x 4 x3 two evaps 2 metres away another condensing unit which was disconnected so originally this room had two evaps two condensing units two 3 horse semi hermitics prestcolds,the pipework had been linked doing away with one compressor/condensing unit as it turned out the compressor running the system was faulty only one piston connected to crank,replaced the unit with a high duty 5 horse all now working fine,the customer took some convincing that my remedy was correct!so in essence listen to customer but do not trust their judgement,my belief when sizing equipment for cold/chiller rooms is oversize build some reserve into them by 25 percent because load factors do change.