Symptoms of a restriction

[Jova007200]

o.O suction pressure approximated near 7PSI avg.... its getting later, I'm omitting things.... eck...

[Gary]

Additional Info :

The system uses an oil separator. Initially, I had its oil drain controlled by a solenoid valve on a delay cycle that only ran once per running cycle. I decided that I botched that badly and changed to a on/off repeat delay. It also pumps down at the end of each cycle for an unloaded start via the thermostat controlled solenoid on the liquid line. Compressor is controlled by low pressure switch.

Why is there a solenoid in the oil return line? I'm wondering if that might cause the separator to act as a condenser/receiver, storing liquid refrigerant... to be unleashed on the system periodically, overfilling and possibly oil logging the condenser? The hunting might be oil working its way through the orifice in short spurts.

[Jova007200]

Why is there a solenoid in the oil return line? I'm wondering if that might cause the separator to act as a condenser/receiver, storing liquid refrigerant... to be unleashed on the system periodically, overfilling and possibly oil logging the condenser? The hunting might be oil working its way through the orifice in short spurts.

Just following manufacturer EBs. The receiver doesn't have a float valve or any type of release within. Oil return could be controlled through a capillary line or a solenoid valve. I chose the solenoid option. The solenoid port is 3/32.

I was considering the possibility that the original relay setting (one on/off cycle) may have allowed too much oil to collect in the separator, causing it to blow out into the system. It would only open during start up, and never again until the next start up. (I know, stupid) The cycle was changed [prior to the problem showing up] to a repeat on/off cycle.

The separator temperature during operation was consistently above the saturation temp. The check valve down stream protected it from back flow upon deactivation. The solenoid valve has always opened at start-up for a few seconds as well, regardless of the cycle chosen.

The hunting was cyclical. It did not appear to be very random. I really felt that it was responding to the bulb conditions.

That said, I did not insulate the separator to protect from off cycle condensing. I considered the check valve and limited amount of refrigerant in that part of the system to be insufficient to cause a problem. I asked an HVAC engineer friend of mine at work if he thought it would be necessary, and he suggested that it was not given the application. So I didn't. Whether or not that was an error on my part is beyond me.


Would you recommend just removing the separator from the equation to negate the possibility you are suggesting?

[Gary]

Yes... I would remove the oil separator. It is highly unlikely that this system would need an oil separator.

[Jova007200]

Agreed.

So, this is what I'm going to do.

• Change the TXV Element
• Remove Oil Separator
• Change Filter Drier

As far as other components, I'm going to hold off on that for now. Given that the TXV can be isolated I'm going to hold off on that for now.

Is this a fair assessment at this point?

[Gary]

Just following manufacturer EBs. The receiver doesn't have a float valve or any type of release within. Oil return could be controlled through a capillary line or a solenoid valve. I chose the solenoid option.

I've never dealt with a separator that didn't have a float. Must be something new. Seems like it could condense liquid refrigerant... and the oil would float on top of that liquid.

[Gary]

Agreed.

So, this is what I'm going to do.

• Change the TXV Element
• Remove Oil Separator
• Change Filter Drier

As far as other components, I'm going to hold off on that for now. Given that the TXV can be isolated I'm going to hold off on that for now.

Is this a fair assessment at this point?

Sounds like a plan.

You might also want to check the pressure/temperature correlation of the recovered refrigerant... just in case.

[Jova007200]

I've never dealt with a separator that didn't have a float. Must be something new. Seems like it could condense liquid refrigerant... and the oil would float on top of that liquid.

Perhaps it should have been a clue when I couldn't find a separator that was properly sized that HAD a float.

Thanks for all of the advice.

[Gary]

You are quite welcome. When you get it going be sure to gather a full set of data so we can evaluate and fine tune the system. You might also find the following link helpful:

http://www.refrigeration-engineer.co...598#post151598

[Jova007200]

I'll surely do that.

One thing, though. It was suggested that I get an element with a MOP charge. I cannot find any 507 elements with such a charge; only for 404a.

Am I missing something?

[Gary]

The purpose of the MOP charge is to protect the compressor from overloading when subjected to heavy loads. Will this system be subjected to heavy loads?

R507 and R404a are very similar. Essentially if you take R507 and add a small amount of R134a, you have R404a.

[Jova007200]

Indeed. I just wasn't sure if it would be an issue if I had to go with a 404a with a MOP Charge if needed.

The most that I would expect the load on the coolant to be is around 1200 Watts. Average load would likely be much less, with a practical maximum of about 1kw.

[Gary]

If the compressor isn't straining (high amps, kicking out on overload, etc.) during pulldown from room temperature, then I wouldn't bother with the MOP charge. Pulldown is the heaviest load, but the loading is limited by orifice size and surplus charge.

Actually, I have yet to see any evidence of a TXV problem.

[Jova007200]

I came to a similar conclusion after the TXV bulb responded to my hand and to a cup of ice. Though, would it be prudent to change to a Z charge given that the C only really controls SH reliably down to -10F or so.

Or is that really not a big deal?

[Gary]

Are you planning on running your glycol down below -10F?

[Jova007200]

Not likely.

So I'll interpret that as a negative regarding the need for a Z charge.