Low suction, high superheat.

[Daveal3D]

Hi guys,
My first post here. We got a cooling cabinet, for cooling dampening solution for a printing press. 2 Compressors- ManeuropMT64 (R22) tandem , it's got plate HE for condensing and a plate HE for evaporating. Head 213 (14bar) Suction 41(2.9bar) at 78°F ambient. Subcooling 8°C, superheat 20°C. TXV Danfoss Tex2. There's an oil separator installed but it's undersized as oil circulates.
Liquid line filter OK and no pressure drop across liquid line. Also there's a suction line filter installed (no pressure drop across it thought).
When i looked at the sight glass i could see the refrigerant running.

I was told that for a system on R22 the suction pressure should be 68psi.

[fireye03]

68 psi=40 degree evap temp,thats mostly air conditioning/comfort cooling applications.

[Daveal3D]

We're cooling dampening solution to 10°C.
We have a cabinet like this one in the next room on 407c and it has 71psi suction 198 head. And it's doing the exact same thing cooling dampening solution to 10°C

[Slatts]

When i looked at the sight glass i could see the refrigerant running.

Gedday Dave. If the system is fully charged you should have a clear sight glass. The fact you can see the refrigerant running in the glass says to me the system is short. That'd explain the low SP and high SH.

There's an oil separator installed but it's undersized as oil circulates.

oil separators only stop about 80% of the oil.

How did you arrive at your SH and SC figures? Just to clear it up for me, you say the suction temperature leaving your evaporator is 12C and your liquid line temp is 32C. is that correct?

[Daveal3D]

Gedday Dave. If the system is fully charged you should have a clear sight glass. The fact you can see the refrigerant running in the glass says to me the system is short. That'd explain the low SP and high SH.


oil separators only stop about 80% of the oil.

How did you arrive at your SH and SC figures? Just to clear it up for me, you say the suction temperature leaving your evaporator is 12C and your liquid line temp is 32C. is that correct?

Suction line temp is 14°C , Liquid line temp is 34°C. SH is 20°C right now & SC is 8°C . I tried adding more refrigerant and only the discharge pressure grew (241psi) while suction was still at 41psi.
8°C SC as far as i know means i have a sufficient amount of refrigerant in the system.

I just started servicing this place. I tried adjusting the superheat and 1 turn made it from 20°C to 3°C and the suction froze over immediately.
My thought were that the TXV is dead. I checked the orifice and nothing was clogging it.

[Slatts]

You shouldn't adjust a TEX2 more than a quarter of a turn at a time.
After that, let it settle for 10 to 20 minutes before checking again.
it sounds to me that it's OK and only needs setting.

[Daveal3D]

You shouldn't adjust a TEX2 more than a quarter of a turn at a time.
After that, let it settle for 10 to 20 minutes before checking again.
it sounds to me that it's OK and only needs setting.

On the same cabinet we got same Maneurop (only on 407c) working on 71 suction and the compressor is cool.
On this cabinet it's working on R22 - 41 suction and the compressors are warm.
Everyone keeps telling me a different story, so do you think my SP is low or normal ?

[Slatts]

On the same cabinet we got same Maneurop (only on 407c) working on 71 suction and the compressor is cool.
On this cabinet it's working on R22 - 41 suction and the compressors are warm.
Everyone keeps telling me a different story, so do you think my SP is low or normal ?

20 is high, 3 is lowish. at 41 PSI your SST is -8. 3K SH will give you a suction temp of -5. You'll have ice on the suction line.
If you can get 3K SH from the system it's working. It looks like your problem is with the load on the system.
I'd suggest you've got a low flow through the evap heat exchanger or it's fowled.

[Daveal3D]

20 is high, 3 is lowish. at 41 PSI your SST is -8. 3K SH will give you a suction temp of -5. You'll have ice on the suction line.
If you can get 3K SH from the system it's working. It looks like your problem is with the load on the system.
I'd suggest you've got a low flow through the evap heat exchanger or it's fowled.

I decided to take a look at the pump pressure and you were right, on the cabinet with the 407c ( 71psi suction) the dampening solution pump reads over 1.5 bars(21psi) , on this cabinet it reads lower than 0.5bar (7.1psi). Both cabinets have the same specs and pumps. Could this be the problem ?

[Slatts]

I decided to take a look at the pump pressure and you were right, on the cabinet with the 407c ( 71psi suction) the dampening solution pump reads over 1.5 bars(21psi) , on this cabinet it reads lower than 0.5bar (7.1psi). Both cabinets have the same specs and pumps. Could this be the problem ?

Most likely. low heat load means low suction pressure. Look for a faulty pump or restricted pipe work or heat exchanger.
Is there a filter in the pick up tube in the dampening fluid tank?

[Daveal3D]

Most likely. low heat load means low suction pressure. Look for a faulty pump or restricted pipe work or heat exchanger.
Is there a filter in the pick up tube in the dampening fluid tank?

Yes, it was clogged with some fibers, i replaced it. I didn't increase the pressure that much, so i checked the pump turns out it's half dead. Overheating, low rpm's, which is not unusual because i was told that this pump was an original that came with the cabinet when they bought it 11 years ago.

I have put an order for a new pump, we'll see than. Should be here within a week.

[Slatts]

Yes, it was clogged with some fibers, i replaced it. I didn't increase the pressure that much, so i checked the pump turns out it's half dead. Overheating, low rpm's, which is not unusual because i was told that this pump was an original that came with the cabinet when they bought it 11 years ago.

I have put an order for a new pump, we'll see than. Should be here within a week.

Good. I think we can call that a win

[Daveal3D]

New pump arrived today, the flow was back to normal, but it hardly had any effect on the suction pressure. It's 45Psi now virtually no difference.
Can the problem be in the TXV ?