A/C pressures and temps

[gregs]

The a/c at work seemed to not be cooling well for a couple of weeks and then got to the point of very marginal cooling. Checked over the normal stuff like filters, made sure indoor and outdoor fans where operating and compressor was running. Even cleaned the coil on the indoor unit and blew out the outdoor unit. On cleaning the outdoor unit I found that it had a sight glass and could see the refrigerant running in it, not solid like it should be and not bubbles. More like watching water running thru a clear hose. Not wanting to be the ac tech, I let them know up front that they should call an ac company to have it checked out and repaired. Tech comes out and puts his gauges on it and starts to check things out. I went over and talked to him briefly just to let him know what I had already done and how it was acting. He finishes up later and I ask him what was wrong. He said it was low on refrigerant and found the schrader valves leaking, but the unit is old needs to be replaced. He will let the owner know and send them out to quote replacing the unit. It works ok in the mornings but doesnt get as cold as it used to in the afternoon. So I decided to put my gauges on it and check the pressures and temps. The sight glass is now full. Its an older R22 system. Here is what I found.

Mid Morning Ambient temp 82 degrees.
High side 220psi/108 degrees -Line temp 86 degrees.
Low side 81psi/48 degrees - Line temp 70 degrees.

Afternoon Ambient temp 89 degrees.
High side 250psi/116 degrees - Line Temp 90 degrees.
Low side 90psi/53 degrees - Line Temp 70.

I am not that well versed in sub cooling and super heat but from what I researched these numbers seem off a little. Wondering if it could be over charged or still undercharged. Or some other issue. I figured I would check it out a little before they called the ac company back as I am guessing they are just going to want to replace it. Any help would be appreciated.

 

[fitter30]

Subcooling and superheat are only accurate with a expansion valve system. Cap tube or orfice systems have to have a charging chart that usually on the compressor excess panel. Looking at your pressure/ temps suction pressure looks high meaning compressor is under a very high load ( house is very hot 90*) or the compressor isn't pumping correctly ( valves in the compressor are not 100%). Take a temp across the evap coil should be between 18*-24*. Weak valves will be less than 18*.

 

[acmikee]

wash your out door coil with simple green and flush it really well then check your pressures

 

[gregs]

It is a expansion valve system. Just for trouble shooting I removed and warmed the bulb to see if it was working. It did act and changed the pressures. So I am guessing that its working.

 

[Climatecreator]

The guy probably over charged the system.....

CC

 

[gregs]

Inside and outside coils have been cleaned prior to the tech working on it.

 

[acmikee]

you said that you blew the condensing unit with air.. wash it with simple green to remove all of the dirt. do you have an amp meter check the amp draw of the condenser fan motor and compressor. also what is your supply and return temps

 

[gregs]

I can wash it out tomorrow. I cleaned the evaporator with some of the foaming non acid coil cleaner. I can check the temps tomorrow as well. I did check a register temp the other day and it was around 60 degrees which seemed warm to me. I will double check tomorrow at the unit with my probe thermometer. I do have a clamp on ammeter if I can find it!

 

[bonneyman]

Time to get a new A/C company. This one is trying to hose you.

Don't let the owner anywhere near the system. If I were you I'd pull the disconnect and not let the occupants run it. The overcharge could slug the compressor and make you need a new system! If they're renters, put 'em up for a few days in a motel. Then get somebody reputable to come out and fix the system.

 

[brewchief]

Subcooling looks pretty high to me indicating an overcharge, superheat isn't terrible so the TXV is doing it's job.

Sent from my SM-G965U using Tapatalk

 

[gregs]

Washed the condenser. Checked the temps after it had time to dry and stabilized. Return temp 75 degrees and supply temp 63 degrees. Looking for my clamp on ammeter.

If it is overcharged any way to estimate how much?

 

[acmikee]

12 deg split did your pressures drop your probably over charged

 

[gregs]

Any way to calculate how much it would be overcharged?

 

[fitter30]

Subcooling should be 10* superheat 10-12* expansion valve bulb should be tight on the line and insulated. Subcooling line temp taken at condenser, superheat right outside of coil cabinet with a thermometer not a infrared thermometer for a accurate reading.

 

[acmikee]

^^^^what he said

 

[Aileron]

Compressor looks weak to me. Suction pressures high for 75 return temp. With a 90 # suction, head pressure seems a little low. I wouldn't trust a sight glass reading for charging a system without a receiver. Refrigerant levels are going to stack up and down in the condenser depending on outdoor temps if its air cooled. Granted for a overcharge your sub-cooling will climb but your head pressure should be high also.

 

[LS6 Tommy]

I'd like to see discharge and return air temps, but the pressures do sound odd.

Tommt

 

[gregs]

^^^^ If you are referring to the indoor air temps, I posted those above 75 return 63 supply. So far I have been using a IR thermometer to take the line readings at the areas that my gauges are connected. I thought both readings where on the high side.

 

[LS6 Tommy]

Duh. How'd I miss that? The high side pressure isn't really all that bad, but the low side pressure is way too high for the supply temp. If you get lower than rated amperage draw, it's probably an inefficient compressor.

Tommy

 

[gregs]

So should it be drawing max amperage with those pressures? I found my clamp on ammeter. How would I go about checking it?

 

[LS6 Tommy]

If the valves are going bad, the suction pressure will be high and the current draw will be lower than the RLA of the compressor. Just clamp your meter to the T2 wire coming off of the contactor and make sure you're not on the wire to the condenser fan. The body of the compressor may be hot and not sweating.
The one thing that doesn't seem to line up with bad valves is the superheat. The line temps you listed indicate low superheat. Low superheat can be from low condenser airflow, undercharge, a stuck open or overfeeding metering device. High superheat indicates overcharge, restricted or underfeeding metering device or bad valves.

Tommy

 

[bonneyman]

If the valves are going bad, the suction pressure will be high and the current draw will be lower than the RLA of the compressor. Just clamp your meter to the T2 wire coming off of the contactor and make sure you're not on the wire to the condenser fan. The body of the compressor may be hot and not sweating.
The one thing that doesn't seem to line up with bad valves is the superheat. The line temps you listed indicate low superheat. Low superheat can be from low condenser airflow, undercharge, a stuck open or overfeeding metering device. High superheat indicates overcharge, restricted or underfeeding metering device or bad valves.

Tommy

He's probably got several things going on. If the comp is bypassing gas then it's been operating in a more and more harmful enviornment. Over time the oil will carbonize and windings will dissolve, and that residue could be clogging up his expansion valve inlet screen.
The tech adding freon didn't help matters.

 

[gregs]

Havent had time to check it out anymore. Have a friend of a friend thats a tech thats supposed to come by and check it out. If I get some time before I will try to get the amp readings.

 

[fitter30]

If the expansion valve was clogged suction would be lower not higher.

 

[Aileron]

Washed the condenser. Checked the temps after it had time to dry and stabilized. Return temp 75 degrees and supply temp 63 degrees. Looking for my clamp on ammeter.

If it is overcharged any way to estimate how much?

rereading this thread this is where I read the return temp, I assumed the pressures qiven in the first post where the same with this return temp. So what was the outcome?

 

[gregs]

Still waiting for the friends tech friend to come check it out. The pressures and temps in the first post where outside at the condenser. The post later on had the air temperatures inside at the evaporator.