How Increase Compressor Cooling w/TXV sys

[David40]

I am working on an old cooler condenser that has dissolving coil fins. (I know replacing the coil would be the best thing to do but that is not an option financially or availability wise) This is causing the compressor to overheat and cycle on it's internal overload. This system uses a TXV in the evaporator. With a fixed orifice or cap tube system I would just increase the charge till I get enough cold evaporated refrigerant coming back to the compressor to keep it cool without actually flooding it with liquid. If fact most A/C systems I work on are designed to work this way.
What can I do with a system with a fixed TXV to increase the amount of cold gas coming back to the compressor? Ideas?
Thanks

[lowcool]

shut the tx valve down a bit

[David40]

Wouldn't closing the valve down cause less cool gas returning? Or maybe I'm approaching this from the wrong direction and by shutting the valve down it would also drop the head pressure and therefore not overheat?

[sterl]

Presumably, the reason you have high temperature return and low total flow (thus the comp overheats) is that you are operating at much more than the nominal temperature difference of the evaporator, that is you comp suction is so much lower than your air temp that you get very warm gas; and the low suction pressure means low mass flow through the compressor.

In the meantime your condenser is now oversized and depending on the rest of the pressure control arrrangement could be storing liquid refrigerant; this will eventually starve the active portion of the circuit and overheat the compressor. Does the circ have head pressure control and a receiver?

What temperature is the gas just upstream and downstream of the compressor? What temperature are you trying to maintain in the cool room? What pressures is the machine operating at while it is operating?

[David40]

This is a good lesson on not making assumptions for me.
After reexamining the system I am not convinced I have a coil problem. Allow me to explain further.

The system: A reach-in cooler running on R-22 consisting of two 2-Ton condensing units supplying four evaporators (2 each) with a TXV in each unit. Operating temp is controlled by a cut-in cut-out pressure switch on each condenser. Defrost is accomplished by condenser off time (no heaters) controlled by a defrost timer on each condenser, which are set at 40 minutes every 3 hours. Also, each condenser has a solenoid valve on the high side that appears to energize during defrost and is also controlled by an adjustable thermostat who's sensing bulb runs through the wall into the cooler. The solenoid valve is off during the cooling cycle regardless of box temperature and seems to only have some purpose during the defrost cycle.
The uncertainty I have is the proper reason/function of the solenoid valve and the thermostat that is tied into that.
Since I have two identical condensers along side each other I made a comparison. With both units running and a box temp of 40 degrees I get almost identical pressure/temp readings except one compressor's can temperature is 129 degrees while the problem condenser's can is at 170 degrees, and the head pressure on the problem condenser (195 degrees) is actually lower than the other one (225 degrees). Both amp out at about 13 Amps and the head pressure. Sop what on earth would make that one can so much hotter? Got me stumped.

PS. I should mention that it looks like the system was modified at some point because there are disconnected temperature switches on the wall near each of the thermostats for the solenoid valves. It looks like the box temp used to be controlled by two thermostatic switches rather than the currently used pressure switches.

[gregd1401]

May be an internal leak on the high side of compressor causing temperature of can to overheat.

[David40]

Yes, I am 99% sure that's what it is.

[goshen]

Yes, I am 99% sure that's what it is.

Hi after reading this interesting post ,all i can say ,is the same ,it would seem like a leak.
Good luck

[oldesky]

Was this originally hot gas defrost? Are the compressors identical? E.G. They may have the same displacement but different motor H.P.Are they running identical Low side pressures? If they are truly"identical" systems The cause maybe different return suction temperatures. I would suggest if the pipe runs are identical that the superheat on the high temp compressor circuit may be too high.