Frost on suction line near compressor

[ctct]

I just installed a new evaporator coil in a walk in cooler. Everything seems to be working fine temp wise, but there is frost on the suction line to the compressor and compressor is cool at that spot. The system is r22 45psi low and 160 high. I suspect I need to adjust the txv for more super heat but didn't want to try as a first option. Anybody have any other ideas. any questions let me know, thanks

[LRAC]

I just installed a new evaporator coil in a walk in cooler. Everything seems to be working fine temp wise, but there is frost on the suction line to the compressor and compressor is cool at that spot. The system is r22 45psi low and 160 high. I suspect I need to adjust the txv for more super heat but didn't want to try as a first option. Anybody have any other ideas. any questions let me know, thanks

Hi ctct

Unless you check your superheat readings you want know, also H/P seems a bit low for R22.

Regards
Lrac

[taz24]

The system is r22 45psi low and 160 high. I suspect I need to adjust the txv for more super heat but didn't want to try as a first option. Anybody have any other ideas. any questions let me know, thanks


The suction Pressure you state indicates that you are evaporating at about -15c. You will get cold gas back at that temp, cold enough to frost the suction. Measure the temp of the suction line as it comes out of the evap, You need to see a temp diff of about +6 to +10.
You do need to measure the actual superheat before you adjust the valve.

Cheers taz.

[davej]

Taz is right it does seem low for 22, with 22 you can charge past the frosting point as the back pressure rises.
check your superheat and probably put some more gas in head pressure should be higher ( maybe around 250psig)

[ctct]

on measuring superheat i'm getting conflicting ways to do it correctly. Some say measure temps with thermometer and others say use pressure conversion chart. There is a schrader on the evap outlet. Anybody want to tell me exactly where and how to measure the temps. The way i checked already shows about 3deg. which is too low if i checked correctly.

[Electrocoolman]

Is your TEV phial sited correctly and is it insulated?

[taz24]

on measuring superheat i'm getting conflicting ways to do it correctly. Some say measure temps with thermometer and others say use pressure conversion chart. There is a schrader on the evap outlet. Anybody want to tell me exactly where and how to measure the temps. The way i checked already shows about 3deg. which is too low if i checked correctly.

You can only truely test superheat by measureing the evap pressure with gauges and then measureing the actual temp with a thermomiter.
You can conect your gauges to the schrader on the evap or use the suction port back at the comp. The pressure drop over the suction line may affect the actual temp but if that is all you have then go with it. You will be able to get exact readings with no pressure drop by measureing the evap itself.

There is a cruder and less acurate way of doing it by measuring the temp just after the TEV and then on the exit of the evap you should see a temp differance in the region of about 6 to 10k.

The thermomiter only method should be used if you can not fit gauges for any reason.

taz.

[LRAC]

This should help you ctct

To measure evaporator superheat:
1) Record the actual temperature at the TXV bulb.
2) Record the evaporating pressure at the TXV bulb.
3) Convert the evaporating pressure to temperature by using those handy
pocket pressure/temperature cards. These cards/charts show the saturation
pressure/temperature relationship for those refrigerants.
4) Subtract the temperature you converted on the pressure/temperature card
from the actual temperature you recorded at the TXV bulb.
5) The difference is the actual evaporator superheat.

To measure subcooling:
1) Record the compressor discharge pressure at the condenser or receiver.
2) Convert the discharge pressure to temperature by using the
pressure/temperature cards.
3) Record the actual temperature of the liquid leaving the condenser.
4) Subtract the liquid temperature (at the condenser) from the converted
temperature (from the discharge pressure using the pressure/temperature
card).
5) The difference is the amount of subcooling.

Kind regards
Lrac

[ctct]

I'll try it that way as well. Also the sight glass still has some bubbles should I charge till it it is clear. Thanks for the help, i'm use to working on car a/c even though all the principles are the same just a few things I don't know about refrigeration.

[Peter_1]

ctct, the way Taz24 and LRAC described how to measure SH and SC is the only right way and everybody who's giving you other conflicting information is wrong.

[ctct]

I should measure the temp at the tev bulb and then measure pressure at the outlet schrader, that is about an inch away. The pressure at the schrader is 46psi the chart on my tank wore away any body know the value for that. Is an infrared therm okb to use. How about the sight glass issue. thanks every body.Also the tev reads 404 or 502 this tev came with the evap that is desinged for and running 22 is there any issues with that

[Pooh]

CTCT
wrong valve fitted you need an R22 valve as the phial charge is wrong. This will make setting the valve correctly impossible.

Ian