Stewie's Chiller Revision 3.0b Build :)

[Xeon th MG Pony]

No thats the test pressure!

It is a low temp compressor thuse the SST (Saturated Suction Temp) of the refrigerant under normal opperating pressur the CPR must be set or the MOP must be set to that pressure and it will be in the 20psi range or so!

[Stewie007]

The warning on the side does not state test... it says operating... Not that anybody uses a low temp compressor for such applications.

I obviously won't be running that high... 20PSI is right around the range I intend upon operating. I'll set the crank at 40PSI. The effective range for this compressor is -40 - 10F.

Still though, why is tuning this system going to be such a nightmare with just a TXV???

[Xeon th MG Pony]

Who said that? Ensuring the compressor will not be over loaded will be a bit of a pain though

[Stewie007]

Well, you answered my question, if it was a bit oddly asked :p.

I just wanted to know why this was essential. I guess Im not grasping how such a low load for the compressor would cause it to overload; that's all.

[Xeon th MG Pony]

lower the tempriture the lower the pressure works at, the lower the pressure less work the electrical motor has to do for compressing the qas (Due to the low quantity of vapour in the cylinder cavity) Thuse low working duty of the electrical motor.

Now at a higher pressure you not have more gas due to a lower specific volume (Higher pressure=More gass moved per piston stroke) and this takes much more energy to compress which will over load the electrical motor in the compressor as it is designed for low temp use, which does not require much force to compress the gas.

Low temp compressors expect the low pressure (Higher specific volume) thus use a wide bor cylinder and larger piston to move the needed amount of gas, being the Specific volume is so high they don't need a more powerfull motor to compress with this bigger piston! BUT if you try to use it as a medium temp, instead of needing a 1/2hp motor you'd need a 1.5Hp motor.

The motor can handle the over load for a verry short periot (IE When it first starts) but with out an MOP valve or a CPR valve the electrical motor will quickly over heat and trip on over load due to the higher pressur and lower specific volume!

[Stewie007]

But I'm not using it as a medium temp. I'm trying to use it for sub-zero evaporating temps.

[DetroitAC]

If you're just trying to get below 0C, that should use a high temp compressor! It's just relative terms in the refrig. biz.

In Tecumseh's terms:
High temp = 45F to 20F (7C to -6.7C)
Commercial Temp = 45F to -10F (7C to -23C)
Medium Temp = 30F to -10F (-1C to -23C)
Low Temp = 10F to -40F (-12C to -40C)

you can also find some Extended range Medium Temps with other mfr, I don't see one listed for Tecumseh.

[Xeon th MG Pony]

But I'm not using it as a medium temp. I'm trying to use it for sub-zero evaporating temps.

To use it in its design range you'd need to be going a hell of alot lower then 0c like -25 but still need an MOP to protect the compressor or a CPR.

[Xeon th MG Pony]

The Max operating pressure of this compressor is 150 PSI........

I guess I'll get a crank then... but I still need the switch right?

I'm going back to comment on this, the 150 is the max allowadle pressure to exist in the low side, just as the Max pressure allowed in the high side is 500psi, idealy neither will ever be reached!

Do not mistake the max working pressures as any thing other then that, proper opperating pressures will be much lower on the suction side and should not exceed 300psi for R-507 on the discharge side!

[Stewie007]

Of course, I was just clarifying that it wasn't test pressure.

To use it in its design range you'd need to be going a hell of alot lower then 0c like -25 but still need an MOP to protect the compressor or a CPR.

But of course. Tis why I'm specing out propylene glycol and still deciding what to mix it with for a -15 - -20F chilled solution. That's what I meant when I said sub-zero

But still, it would probably be better to do as you say anyways. That'll give me the ability to run it at different loads, should I decide to change things later.

[Stewie007]

Note..... I think I finally understand ... here months later. :-p

[Stewie007]

If nobody sees this I'll start a new thread, but I'd rather not.

I'm looking for the maximum operating pressure of my compressor, which is a Tecumseh AJA2419ZXA. I looked at the data sheets, and I'm not certain. There is a value called Return Gas in these data sheets, and it says 40. I don't know if that means 40PSI is the pressure rating for the suction side.... or if its a meaningless number to me.

I'm going to get a crank case valve to fit up here. Let me know. Thanks.