R22 WALK-IN COOLER LOW PRESSURE STAYS SAME AT ALL TIMES.

[ptair]

Hi everybody. I am an HVAC/R tech with 7 years of experience in trade. I have done so many heating and cooling service calls and and installations, but when it comes to refrigeration services not so many.

I had this service call yesterday: Customer was complaining about compressor being loud at start up. I check the condenser and see condensation all over the compressor and water all around the condenser that indicates unit is overcharged.

I put my gauges on the unit, low side shows 65 psi and high side around 350 psi. I had my helper change raise the temperature on the thermostat to see solenoid and pressure control work properly. Low side pressure stays the same at 65 psi and high side rises to almost 475 psi as he raises the set temp. Basically, high pressure switch turns off the system because low side pressure stays above 60 psi at all times.

I do not hear solenoid valve clicking when the thermostat kicks on or off. It seems like a bad solenoid but it just blows me off how high side pressure goes crazy high and low side pressure stays the same.

Has anyone ever came across a problem like this?
I appreciate any help in advance.

[Red Man]

Did you measure sub cooling?

[ptair]

No I did not. It just kind of blew me off that suction side pressure just stays the same at all times. Since the unit was cooling the box I postponed the service and left for next service call. Suction side pressure was 65 psi unit on or off, box temperature was 38 degrees, condenser ambient temperature was 75 degrees. I have to go back tomorrow and look into it more deeply, I will check subcooling and superheat but I just wanted to see if anyone can give a clue with low side pressure not changing unit on or off.
Thank you for your response.

[TechmanTerry]

What refrigerant? Excessive refrigerant.?

[ptair]

R22 refrigerant. Yes definitely seems overcharged. Business owner said some other company serviced it 6 months ago.

[Red Man]

65 psi R22 saturation temp is 37.5. Hard to believe it’s cooling the box at that saturation temp, maybe keeping it in the low 40s. Also you have no superheat. I’d expect to find high subcooling. Sounds likely overcharged. The reason the suction pressure doesn’t change when the solenoid valve closes is because the compressor doesn’t stay running long enough. There is too much refrigerant to pump down so the high pressure switch trips before the suction pressure can drop. I would start by removing enough charge to get a reasonable sub cooling and see if it will pump down. Then troubleshoot from there. I’d suspect a misdiagnosed problem leading to the unit being overcharged.

[ptair]

Red Man. Thank you for your reply. I appreciate the help.

[GenesisRefrig]

Indoor condensing unit, or outdoor? Does it have a headmaster control for low ambient operation?

I agree, pull charge until you have 70%-80% receiver level, and go from there.

[VTP99]

How big is the receiver and what size is the compressor ?

[ammoniadog]

I'm not entirely sure why Red Man keeps talking about subcooling, since subcooling data is mostly worthless on a system with a receiver.

Basically if the receiver is empty you will have zero subcooling. Then once the sight glass clears you will have a small amount of subcooling that will stay the same no matter how much more refrigerant you dump in, until you completely fill up the receiver. Then the subcooling will go crazy.

I suspect he is right about the system being way overcharged with a completely full receiver. His description of what's happening when it tries to pump down sounds like what is probably happening.

I would slowly remove refrigerant until it can stay running without the discharge pressure going nuts. If the condensing unit is indoors then I would probably recover some refrigerant until the sight glass starts to bubble, then add some back in until it clears, then add just a little more and call it good.

If the condensing unit is outside and if it has a 3 way valve (headmaster) between the condenser coil and the receiver then you need a little extra refrigerant for it to work properly during cold weather. One method to do this involves running a Mapp gas torch up and down the receiver several times and then using the back of your hand to find where the liquid level is inside of the receiver.

Use a piece of cardboard or something to block part of the condenser coil to try to simulate the head pressure that you might find on about a 100 degree day. Then torch the receiver and adjust the charge so that the reciever is about 3/4 full. Then satisfy the thermostat and make sure the thing can pump down and torch the receiver again to double check that it's still OK. Then you should be good.

Of course what you said about not being able to hear the solenoid open and close might be a different problem, or maybe it's just a really quiet receiver.

Keep us posted on what you figure out.

[Red Man]

I'm not entirely sure why Red Man keeps talking about subcooling, since subcooling data is mostly worthless on a system with a receiver.

Basically if the receiver is empty you will have zero subcooling. Then once the sight glass clears you will have a small amount of subcooling that will stay the same no matter how much more refrigerant you dump in, until you completely fill up the receiver. Then the subcooling will go crazy.

I suspect he is right about the system being way overcharged with a completely full receiver. His description of what's happening when it tries to pump down sounds like what is probably happening.

I would slowly remove refrigerant until it can stay running without the discharge pressure going nuts. If the condensing unit is indoors then I would probably recover some refrigerant until the sight glass starts to bubble, then add some back in until it clears, then add just a little more and call it good.

If the condensing unit is outside and if it has a 3 way valve (headmaster) between the condenser coil and the receiver then you need a little extra refrigerant for it to work properly during cold weather. One method to do this involves running a Mapp gas torch up and down the receiver several times and then using the back of your hand to find where the liquid level is inside of the receiver.

Use a piece of cardboard or something to block part of the condenser coil to try to simulate the head pressure that you might find on about a 100 degree day. Then torch the receiver and adjust the charge so that the reciever is about 3/4 full. Then satisfy the thermostat and make sure the thing can pump down and torch the receiver again to double check that it's still OK. Then you should be good.

Of course what you said about not being able to hear the solenoid open and close might be a different problem, or maybe it's just a really quiet receiver.

Keep us posted on what you figure out.

I’m definitely in the camp of sub cooling is what it is with a receiver...I typically see 2-5 degrees. Maybe your comment was sarcastic? In this situation, since the head pressure is elevated so much, I suspect the receiver is completely full and I suspect the sub cooling would be crazy. Of course it would need to be measured to confirm.

Seems to me like the solenoid valve must be opening and closing, why else would it trip on high pressure shortly after he tries to close it?

[VTP99]

Well if it was truly over charged 6 months ago that's one tuff compressor.
Also that TEV could be a hard shut off type.

[TechmanTerry]

What would your AC hiside press be w/ a 75*F ambient? Pretty much the same for a "R" system on a 75*day. Start there and then see how the other readings match up.

[pecmsg]

Have you tried pumping down with the suction service valve?

[Olivero]

Just logically speaking, the box wouldn't be cooling and the suction side would be 0 if the solenoid was not working.

Sounds overcharged to me.

[ptair]

I appreciate all of your replies. It was an indoor condenser unit with no headmaster, has a 2 hp 24k btu Tecumseh compressor. I went back today and started recovering refrigerant couple of pounds at a time until I had 4 degree of subcooling. This unit was insanely overcharged. After removing 14 pounds of refrigerant. I had 48 psi suction pressure with 12 degree superheat 205 psi high side pressure with 37 degree box and 75 degree ambient temperature. Even that sight glass was clear and Txv had perfect superheat some ice started forming on evap distributor tubes. Evaporator is clean, all fans are running correctly. Is this normal since evap coil is running below freezing point?

[pecmsg]

I appreciate all of your replies. It was an indoor condenser unit with no headmaster, has a 2 hp 24k btu Tecumseh compressor. I went back today and started recovering refrigerant couple of pounds at a time until I had 4 degree of subcooling. This unit was insanely overcharged. After removing 14 pounds of refrigerant. I had 48 psi suction pressure with 12 degree superheat 205 psi high side pressure with 37 degree box and 75 degree ambient temperature. Even that sight glass was clear and Txv had perfect superheat some ice started forming on evap distributor tubes. Evaporator is clean, all fans are running correctly. Is this normal since evap coil is running below freezing point?

Unfortunately you have no way of knowing what refrigerant(s) are in there. Consider recovering the entire charge, change the drier, evacuate and recharge with fresh R-22.

[icemeister]

...It was an indoor condenser unit with no headmaster, has a 2 hp 24k btu Tecumseh compressor. I went back today and started recovering refrigerant couple of pounds at a time until I had 4 degree of subcooling. This unit was insanely overcharged. After removing 14 pounds of refrigerant. I had 48 psi suction pressure with 12 degree superheat 205 psi high side pressure with 37 degree box and 75 degree ambient temperature...

I've followed up behind numerous others who obviously had little refrigeration experience and who had severely overcharged the system with results just as you describe.

On one such occasion, following up after a local A/C service contractor, I found the reason why, clearly written in Sharpie on the Larkin 5 hp R12 condensing unit:

"System has TXV. Must be charged to 13°F subcooling."

I recovered about 40 lbs from that one.

[VTP99]

I recovered about 40 lbs from that one.

Ohh boy that's a lot of R12 liquid gold today.
So you never had to sell that customer R12 again or did it mysterious disappear never to be seen again ?

[Red Man]

Are you asking if ice on distributor tunes is normal? It is normal.