Display freezer problems!

[cretan]

I have been working on a display freezer with a semi hermetic compressor.404a.It has a expansion valve and no reciever tank or a cpr valve.does this sound normal to you?by the way..the compressor just failed.

[Toolman]

You need a CPR for start up after defrost to keep the pressure down at the compressor , you might get away with no CPR but no receiver doesn't sound normal . Although it will still work if it doesn't need more gas than the condenser can store . It's usually not enough gas that's why they have receivers. Hows the gas charge in the sightglass look ?
Add a receiver check your gas charge and a CPR for good measure . Have you checked the capacity of the system ? If it has been installed like that it ( the compressor ) may be undersized because there are plenty of clowns who guess on the size and if the clown who put it in didn't fit a CPR or receiver its more than likely theres more issues than a CPR & receiver

[cretan]

Thanks for the reply.there is no sight glass on system.pressure on low side(after defrost) was over 100 psi.the compressor crapped out yesterday.I am sure there are parts missing fron this system.

[Dan]

Hi Cretan. Some manufacturers (Hussmann comes to mind) use an empty filter drier shell as a receiver. It looks like you have two driers installed in the liquid line. Any chance that's what you have?

[cretan]

hey Dan.Yes there was a empty filter drier shell on this system.I was told it was a "discharge muffler" and removed it.what effect does removing it have on the system?also the low side pressure is too high after defrost.what would cause that?Wrong expansion valve possibly? Thanks

[Dan]

If you do not have a CPR valve, the manufacturer may have relied on a MOP (Maximum Operating Pressure) TEV (Sporlan ZP charge, for example). Check the powerhead. If it is not a ZP charge - or another manufacturer's equivalent, change it to one. Best thing, however is a CPR valve.

If you took out the empty shell, you will not be able to charge correctly for TEV operation. The excess refrigerant storage during low load conditions will be in bottom passes of the condenser.

[Toolman]

Hi again , you said the system was SemiHermetic and it has No sightglass & no real receiver just a lump in the liquid line ( empty drier shell ) .I imagine a system that has a SemiHermetic to have a decent set up hanging off it but this one sounds like its the bare arse version . Maybe its a critical charge system? In that case you need to find that amount and charge exactly . SemiHermetic system isnt usually a small one . What capacity compressor are we talking about ??

[cretan]

What capacity compressor are we talking about ??1.5 H.P.....semi herm.6300 btu from what I can remember. ..........
If you do not have a CPR valve, the manufacturer may have relied on a MOP I will re-install the empty shell and I will add a cpr.Are they set to a certain pressure?I have never installed one.thanks for the help guys.no-one else has been able to help me up till now.

[lana]

Hi cretan,

Some points :

1- Discharge mufflers are installed on the discharge line between the compressor and the condenser. Receivers are installed after the condenser.

2- It is the best way to have a receiver for systems with TEV. However, you can have DX system without receiver but the refrigerant charge will be critical. As Dan mentioned the excess refrigerant will be in the condenser.

3- CPR and TEV with MOP do the same thing. Preventing high pressures in the compressor during high loads. I suggest you use one of these options.

4- I don't agree with this statement by Toolman. If I understand it correctly.



It's usually not enough gas that's why they have receivers.


Receiver is used to store excess refrigerant. If there is lack of refrigerant then what can the receiver do to correct it?

Good luck
Cheers

[Toolman]

Although it will still work if it doesn't need more gas than the condenser can store . It's usually not enough gas that's why they have receivers.

IANA - Heres the whole statement above , I was talking about the system and its required charge and how no receiver will work if it doesnt need more than the condenser can hold . :rolleyes:

CRETAN - Set the CPR by having a very low pressure at the compressor when it comes off defrost , basically the CPR closed and adjust open when the system comes off defrost. You will here it and see it ( on the gauges if you have a gauge before and after CPR ) eg: choking the pressure back against the valve plate. :D

[lana]

Thank you Toolman for clarifying that.
Cheers

[cretan]

i DECIDED to install a zp charged head on the txv.I removed all the ***** from system.the plate on the freezer says it takes a 42oz charge.I got to 25oz and head pressure was at 250psi.I left it like this and it seems to be working fine.I manually put it into defrost for half hour then started it and there was no hard starting.Thanks to all for your help.

[Toolman]

I have been working on a display freezer with a semi hermetic compressor.404a.It has a expansion valve and no reciever tank or a cpr valve.does this sound normal to you?.

Its nice to here you got it going but........25oz gas charge on a Semi-Hermetic system with TX valve - you are very lucky you got that going , I have never heard of a SemiHermetic system having such a tiny amount of gas . It must be the worlds smallest model and smallest evaporator ?:eek:

[cretan]

Its nice to here you got it going but........25oz gas charge on a Semi-Hermetic system with TX valve - you are very lucky you got that going , I have never heard of a SemiHermetic system having such a tiny amount of gas . It must be the worlds smallest model and smallest evaporator ?:eek: No kidding!Its a 1.5 hp semi hermetic.with the recomended 42oz charge it slugs the compressor when it comes out of defrost.this was the only way to get it woking properly.

[Toolman]

No kidding!Its a 1.5 hp semi hermetic.with the recomended 42oz charge it slugs the compressor when it comes out of defrost.this was the only way to get it working properly.

I'm sorry when I here ounces 25 Oz converts to 0.71 KG ( we use metric system in OZ ) I thought geez thats a tiny amount of gas but I suppose its not that tiny .
Is your freezer cabinet a glass topped sliding door type with 3 doors ? If so its an old Hussman cabinet and is a critical charge . Sounds like you have pretty well sorted it , Seeya :D

[cretan]

it,s a stand-up 3 door freezer.1.5 h.p.has an expansion valve,with no reciever,no cpr valve,404a.I have a few more grey hairs thanks to this unit.