Broken compressors since refrigerant change

[zeus2k6]

Hi fellas,
Im a maintenance engineer for a firm and have across this strange problem of frequent breaking down of ac compressors in our ac system. We are using Carrier 5H120 compressor with unknown condenser. The expansion valves are Danfuss TES12 and we are using 16 of those. The suction pressure in compressor if about 50psi and the discharge pressure is about 220psi. Apart from that I have absolutely no other data.
The problem is, that 6 months ago we changed out the refrigerant from R-22 to R-404A and since then the compressors have started breaking down. We changed out the expansion valves also to suit the new refrigerant but did not change anything else.
A carrier technician once told us that it is because of the high discharge pressure created by R-404A but i very much doubt if it is the case because the gauges on the compressor still show 220-260 psi of discharge pressure, which i think are pretty much tolerable.
We have had to replace numerous broken pistons and some compressors totally! but we still dont have a clue as to what has suddenly gone wrong with the system!
Any help will be appreciated!
Thanks

[powell]

Many H22 compressors, 0 to 45 F SST are also medium temp R404A, -5 to +25 F SST,depending on the compressor, if you change to POE oil. I'll try to check out the Carrier 5H120 specs.

So it would seem that you now have a medium temp compressor in a high temp application. Could be trouble. 50 psig relates to about a +16 F SST using R404A, it should be about a +45 F SST for A/C.

Did you change the oil to POE? Second, busted pistons are usually a sympton of liquid flooding.

I think you need to rethink this conversion.

[lana]

Hi there,

Dear zeus2k6,

Powell provided you the answer. If you did not change the oi,l and I must say according to a proper procedure, then you have a contaminated system which obviously breaks down.

Your compressor service company will be able to tell you what the reason is for breaking down. Is it liquid flood back or lack of lubrication?

Good luck.

Cheers

[The Viking]

OK,
Let's stress this one more time..

Mineral oil requires the Chlorine in the old fashioned refrigerants (like R-22) to keep it's viscosity and be able to lubricate.
As modern refrigerants (like R-404a) lacks Chlorine, they requires synthetic oil or there will be problems....

(And your systems, originally designed for R-22, will most likely have been supplied with mineral oil)

Also, whoever changed the expansion valves should have ensured they operated correctly, with a superheat to protect the compressors from flood back.

[Gary]

Is this a parallel compressor (rack) system? Or are these individual systems? Or a single compressor with 16 evaporators?

The suction pressure is running much too low.

And as others have pointed out, you need synthetic oil.

[powell]

Here's the link for the compressor specs. It's interesting that Table 1 lists the capacity for R404A at a 40 F SST but Table 12 on page 17 shows a maximum SST of 20 F.


http://www.carlylecompressor.com/Fil...h_09rh-2xa.pdf

[US Iceman]

It's interesting that Table 1 lists the capacity for R404A at a 40 F SST but Table 12 on page 17 shows a maximum SST of 20 F.

Those are just distinct operating points that list the performance of the compressor. That's all those are. These have nothing to do with the operating limits or application requirements.

zeus2k6,
On the other comment of 16 TXV's being replaced...did someone try to adjust the valves after they were installed?

[Gary]

Lacking sufficient information for a firm diagnosis, I am guessing that the unloaders are set for 50 psi, which is borderline acceptable for R22 and way too low for R404A. The unloaders should be set to at least 70 psi.

[hendry]

yeah, i feel you should look into the procedure/s which has been used in the conversion.
may be, from the overall works performed you'll find some inconsistency with the recommended practice for refriegrant coversion program (RCP).

do anticipate the problem/s already inhibit in the system prior to conversion.

cheers ....

[zeus2k6]

Thanks for the input guys. I checked the oil specs, it has been changed over to a synthetic oil called Emkarate RL 68H. So, I think now we can rule out the possibility of wrong oil.
To answer a couple of more queries, we are using one compressor to run all the 16 expansion valves. Also, the heat exchangers (sea-water cooled) were not changed out as a part of upgrade and continue to remain the same. Also, there are absolutely no gauges on the condensers, so i cannot tell if they are working fine or not.

[powell]

Those are just distinct operating points that list the performance of the compressor. That's all those are. These have nothing to do with the operating limits or application requirements.

US Iceman,

Yes, I understand these tables are just distinct or common operating conditions. But I have not seen where this type of chart listing multiple evap temps sway far from the actual compressor performance charts where the SST, CT, RGT, LLT and OAT fine tune the actual operating limits or application requirements.

But I am much more familiar with Copeland than Carlyle open drive compressors.

I've done some research on this 5H120 and I have not found where it is rated above a +35 SST with R404A, I'm probably missing something though because he did state that a Carrier tech was involved.

Regards.........Powell

[Gary]

It seems we have narrowed it down to an unloading problem.

This compressor should be capable of unloading down to 25% of capacity.

The pressure should never reach 50 psi, unloading itself along the way and then shutting down the compressor on low pressure control slightly below the lowest unloading pressure setting.

Running the pressure this low can freeze coils, flood the compressor and break things.

[zeus2k6]

Im quite new to this refrigeration and A/C and dont quite get all of the terms that you people use . So if it is an unloading problem then what you mean to say is that there is a problem at the expansion valve, right? Then we need to reset the setting so that the suction pressure on the compressor stays atleast 70psi. Also, if thers is any automatic shut-off mechanism on the compressor (ill have to find out if there is) then that needs to be set to a pressure of 65-70 psi so that the compressor shuts down if the suction pressure goes below 70psi.
Also, if we increase the pressure at suction side then that would mean lesser cooling and probable we would have to consider more refrigerant and compressors for cooling the space, correct?
Thanks for all the info guys. I think now I should be calling in for some carrier expert to give his suggestion. Atleast ill understand what all he means when he says something .

[Gary]

Im quite new to this refrigeration and A/C and dont quite get all of the terms that you people use . So if it is an unloading problem then what you mean to say is that there is a problem at the expansion valve, right? Then we need to reset the setting so that the suction pressure on the compressor stays atleast 70psi. Also, if thers is any automatic shut-off mechanism on the compressor (ill have to find out if there is) then that needs to be set to a pressure of 65-70 psi so that the compressor shuts down if the suction pressure goes below 70psi.
Also, if we increase the pressure at suction side then that would mean lesser cooling and probable we would have to consider more refrigerant and compressors for cooling the space, correct?
Thanks for all the info guys. I think now I should be calling in for some carrier expert to give his suggestion. At least ill understand what all he means when he says something .

Unloading is at the compressor, not the expansion valves. Leave the expansion valve settings alone. Any attempt to raise suction pressure by adjusting the expansion valves will make the problem worse, not better. The purpose of the expansion valve adjustment stem is to adjust superheat NOT pressure.

In the manual supplied by Powell in an earlier post, the unloader information starts on page 19. If you don't fully understand it, then you should not adjust it.

No, you will not need more compressors or refrigerant to cool the space... and yes it is time to call in the experts.

[get the gauges]

Hi fellas,
Im a maintenance engineer for a firm and have across this strange problem of frequent breaking down of ac compressors in our ac system.

Is it me or is anyone else wondering why the R22 has been changed for R404a, i'd of been going for R407c for an A/C application,has some one mixed up the 4's? at 50psi the evaporating is -10degC .Is it the unloaders that will sort the back pressure out ? Why make life so hard by changing the temperature of the gas, the back pressure would have to be up at 74 psi to get 0degc evap temp, to stop the unloader coming in and out so much you could be up at 80psi before reloading What am i missing ?

[Gary]

Is it me or is anyone else wondering why the R22 has been changed for R404a, i'd of been going for R407c for an A/C application,has some one mixed up the 4's? at 50psi the evaporating is -10degC .Is it the unloaders that will sort the back pressure out ? Why make life so hard by changing the temperature of the gas, the back pressure would have to be up at 74 psi to get 0degc evap temp, to stop the unloader coming in and out so much you could be up at 80psi before reloading What am i missing ?

In order to simplify their maintenance, it is not uncommon for large sites, such as supermarket chains, to want the same refrigerant in all of their equipment. While it may not be the best choice for some applications, R404A or R507 (which is almost the same thing) is a good all purpose refrigerant.

[US Iceman]

So if it is an unloading problem then what you mean to say is that there is a problem at the expansion valve, right?

No. However, I think this is where your problem with broken compressors started.

I suspect the change in refrigerant and the different vapor pressures of the new refrigerant are at the heart of your problem. The compressor unloading (capacity control) was probably not adjusted to compensate for the new vapor pressure. As a result, at part load the compressor was reacting to different conditions which where probably affecting the TXV's causing them to hunt.

When a TXV hunts it cannot control superheat and some liquid refrigerant entered the compressor as a result.

In Carlyle compressors you have to change the unloading spring in the compressor. These springs are refrigerant dependent and have different spring tensions which affect the unloading mechanism.