Prestcold compressor

[caramelsoul]

I have a problem with my freezer system.

Plant record as follows...

Compressor Delivery Pressure - 13.5bar
Compressor delivery gas temp - 97c
Liquid Line temp - 31c
Product Cooled (Room air) temp - -12c
Compressor suction - 1bar
Liquid line sight glass clear and dry. The room temp is meant to come down to -21, but am only achieving -12 to -14. Refrigerant is R417A. Cant find much wrong with it myself, any suggestions?

[NoNickName]

It looks like refrigerant is a drop in replacement of R22. If this is the case, did the system achieve -21°C with R22?
What is the expected capacity against the actual heat load?
From the discharge gas temperature I see that you probably have a high suction superheat. How much is SSH and suction temperature?

EDIT: 1 bar suction is -40°C therefore there is definitely something wrong with you evaporating to suction side.

[caramelsoul]

The system achieved -21 with R22 and it also used to achieve it with the R417A.

Can you expand on the question - What is the expected capacity against the actual heat load? -

Suction temp is 9c. How do i work out suction superheat?

Do you think there might be something wrong with evaporator?

[NoNickName]

Yes, there is something wrong definitely.
1 bar(g) corresponds to -25°C saturated liquid.
The suction temperature is 9°C.
The suction superheat is 9-(-25)=34K which is way too much.
The high SSH is a symptom of a starving evaporator.
I suspect the system is low on gas or the TEV closed or filter drier clogged.

[caramelsoul]

What temperature difference would you expect over the filter drier? I have a 6 degree C difference.

[NoNickName]

I would expect ZERO. You have a clogged filter.

[caramelsoul]

Thats what im thinking, i appreciate your help.

[NoNickName]

I would appreciate if you could feed us back after you inspected the drier filter

[caramelsoul]

I have one ordered and it is getting flown out on a helicopter on Friday, i will let you know once i have changed it out.

[NoNickName]

I have one ordered and it is getting flown out on a helicopter on Friday, i will let you know once i have changed it out.

You're on a drilling rig? :off topic:

[casstrig]

Please measure the temperature of the compressor heads as I suspect you have a faulty valve.

[caramelsoul]

The temperature on the compressor heads did seem quite high. Are you talking about taking the temperature off the casing over the pistons? One side of it is a lot higher than the other side, 117 degree C and a bit discoloured which i was putting down to heat.

[caramelsoul]

You're on a drilling rig? :off topic:

On an oil production platform.

[NoNickName]

The temperature on the compressor heads did seem quite high. Are you talking about taking the temperature off the casing over the pistons? One side of it is a lot higher than the other side, 117 degree C and a bit discoloured which i was putting down to heat.

This is normal. One side of the head is the suction, the other side is the discharge. Just like in a car engine, the suction side is colder, the exhaust is warmer.
The high discharge temperature is in turn caused by the high suction superheat. Once you rectify the SSH, the discharge temperature would also reduce.

[sefuss]

I have used an R22 replacement gas known as MO29 (R422D) and ive found that i need to add 20% extra when charging the system, ive not used 417a but it may be worth checking if this rule applies to this gas as well here is a link to help you
http://www.gas2010.com/retrofit-hfcs

cheers

[caramelsoul]

Iv changed out the filter drier and there is no difference to the system.

[NoNickName]

Was it dirty or clogged? Have you still got that high temperature drop across it?

[caramelsoul]

No, wasnt dirty and still have a slight temp difference of about 4 deg c across it.

[NoNickName]

I still think there is some occlusion somewhere on the liquid line. Was there much oil inside the filter?

[caramelsoul]

No, hardly any.

[caramelsoul]

TEX problem maybe?

[old gas bottle]

i trust its a R22 expansion valve and not R502 or R404A, that would account for the premature shutting down,

does the suction gauge flutter when fitted,could be valve reeds, R22 makes the heads run hot unless its got the suction valve on the rear case, i would get a head set and have a look if you cant find anything else.;)

[caramelsoul]

It is an R22 expansion valve, but its not prematurely shutting down, its constantly running because its not getting down to desired temp.

Suction gauge does not flutter.

[old gas bottle]

its not going to shut the compressor off but somethings not adding up here, 9deg c suction temps to high and sounds like the TEV is shuting down before the evaps cold enough,try either opening the superheat up a bit or change the valve and check the orafice size.

[NoNickName]

Yeah, I confirm the problem is along the liquid pipe... txv maybe