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Leo1967
27-06-2007, 07:07 AM
Hi everyone!
Yesterday i went to see a friend on a site where there are three McQuay water chillers mod pfs 250 c xe
he told me they where working fine except one that has a noisy comp and while working there's no difference in pressure between discharge and suction.Well,i found something strange in the way the others work as the discharge pipe is almost cold,only 33c! the gouge reads 20 bars and the suction one reads 9 bars.the chillers run on R410A.Shame i didn't have my tools with as i would have liked to take better readings.......has anyone come across something like this before?
thanks in advance

mohamed khamis
27-06-2007, 11:18 AM
Hi everyone!
Yesterday i went to see a friend on a site where there are three McQuay water chillers mod pfs 250 c xe
he told me they where working fine except one that has a noisy comp and while working there's no difference in pressure between discharge and suction.Well,i found something strange in the way the others work as the discharge pipe is almost cold,only 33c! the gouge reads 20 bars and the suction one reads 9 bars.the chillers run on R410A.Shame i didn't have my tools with as i would have liked to take better readings.......has anyone come across something like this before?
thanks in advance

Hi Leo1967

The chiller unit which is working nosily with no difference in discharge and suction pressure is its compressor most likely to run in reverse rotation and u should change the electrical connections properly and ensure about their positions correctly. Otherwise there is a blockage of debris inside the compressor brakes the rotation and prevents the compressor to generate the required pressure difference.

Regarding to the other units, there is an unloading system in these units ?. The condensers of these chillers are water-cooled condenser type with cooling tower?. I made roughly estimation and it is supposed for the discharge temperature to be above 65°C. Could u cite the more data to be helpful.


Cheers

TXiceman
27-06-2007, 03:30 PM
Number one thing to do is to check motor rotation. Next it is generally bad to run a screw in reverse direction as the thrust bearings are not designed to take much reverse thrust.

If the screw is noisy, I'd suggest you get some vibration readings on it and shut it down until you have a course of service diagnostic actions.

If the compressors have a suction block valve, it should hold and you will have excessive pressure in the suction if it is running in the reverse direction. the compressors I have seen that had this happen were destroyed.

ken

absrbrtek
29-06-2007, 01:37 AM
If the screws running you've got basd gaterotors in it, same as a JE Hall single rotor screw. The design on the PFS was really bad. McQ stopped producing them in the US. They tried running them with a 1% to 2% oil concentration in the units but had excessive failures with the screws. If you add refrigerant, add oil or you'll toast the screws. JMHO