compressor question

[nwtch]

I am trying to figure out what the problem is with one of my York RTU's. It sometimes trips out stage 1.
My low side pressure is 61 psig
My high side pressure is 240 psig.
My temp on the suction line is 79.5f
My avg. amps at the compressor is 5.2
My low side temp is34f. Am I correct in thinking that my superheat is approx. 45f?
The refrigerant pressures are moving slowly. I am wondering if I have bad valves in my compressor, or do I need a txv? Is is possible that there is non-condensables in my system?
I have only been doing this work for a couple of years, and this has thrown me a curve.
Any advise will be appreciated.
Thanks, nwtch:

[toy501]

Superheat is high. I would check subcool & if higher than normal I would suspect bad TXV(lost bulb charge or ext. equilizer plugged or liquid line restriction. Test the TXV bulb w/ your hand & see if any pressure changes on your suction pressure.

[lwarren]

If you had bad valves you would have a low head and a high suction. Your Superheat is high. What is the subcooling, ambient temp, supply and return temps, etc.

When does the unit trip, at night, when it starts in the morning, durring the day?

What is tripping, low press, high press, thermals in comp? With your superheat that high i would not be surprised if the compressor is getting to hot and opening the internal thermal overload.

Need alot more info for proper evaluation.

[acam027]

What exactly is tripping, Overload, fuse, board? What is your ambient? what is your delta t? what kind of metering device do you have? Without these questions answered it's pretty hard to answer what is going on without assuming.

[nwtch]

Thanks to all of you for your responses. It looks as though with all of your questions to my problem, I have a lot more research to do. Now I know more about what to look for than previously.

[Defrost]

You said your suction line is 79.5f and your low side is 34f ??????????
Did you mean 79.5f discharge line, 34f suction line temp ?

[51fitter]

Thanks to all of you for your responses. It looks as though with all of your questions to my problem, I have a lot more research to do. Now I know more about what to look for than previously.

I agree nwtch I got dizzy reading all the questions they asked but you are on course. What kind of york unit is it? One of the standard stop n shop plaza units that are around 10-20 tons about 3 years old? Or is it something older? Get the lockout codes (if any) then go from there. The more info the better. Exactly what they said. :)

[nwtch]

my suction pressure is 61f. the guage is showing 34f. the temp of my suction line is 79.5 according to my temp meter, which to me indicates a very high superheat. the ambient temp today was 77 at the time I took these readings. The unit is tripping out sporadically, and not neccessarily every day. Today it did not trip out. So I can't check all of the safetys until it does ita again. The coil isn't freezing up, so at this point I can't really give anymore info. I will be on it again tomorrow. This unit has a model #d3cg090n13046ece. It is an older unit made in approx. 91, I'm pretty sure it has a 60,000btu capacity. So it isn't a very large unit. I don't know if this will help anyone, but it's all I know for now.
Thanks to everyone, nwtch
this unit is so old that it doesn't have any codes, or lights on the board

[makinmoney]

What are you resetting? Is it a manual reset or are you cycling power to the unit to reset the motherboard?

[nwtch]

I am simply cycling the power, and resetting the motherboard. After I do this it will run for a day or two. Someone told me that it may be a freezestat opening. It just seems strange to me that when I start the unit, the pressures increase very slowly, instead of a normal type of increase. I thank you. nwtch

[heatingman]

alot of boards have trouble lights, read them before reseting

[Defrost]

I am simply cycling the power, and resetting the motherboard. After I do this it will run for a day or two. Someone told me that it may be a freezestat opening. It just seems strange to me that when I start the unit, the pressures increase very slowly, instead of a normal type of increase. I thank you. nwtch

If your pressures are rising extremely slow, is it possible you have a restriction somewhere on the low side? Is there a drier on the suction side, it could be restricted. Did someone recently replace some of the components? Maybe sweated some joints without nitro through the system to clean out the pipes.

[nwtch]

no one has broken into the lines in the last two years. before that, I don't know what happened. The only other thing I did was to replace a condenser fan. The unit worked for over a year without any problems after that. It makes sense to me that I have a restriction of some sort. could the unit be over loaded with refrigerant? Would this cause a reaction like I am describing? I could recover the refrig. and see how much I have. Stage 2 is working ok, and I am getting cooling until stage 1 quits. then the unit won't keep up with the heat load. I am cooling a copy room with a lot of copiers that put out a lot of heat. Therefore I am cooling year round. In the winter with an economizer. Thanks nwtch

[damedi07]

it almost sounds like you have a restriction.....the head pressure seems a bit high, but it may be restricted and overcharged. what's the subcooling? RLA?

[51fitter]

When is the last time the cond coil has been cleaned? If you have a double coil you'll have to separate the two coils and hose them down good. Then check your hi/low side's again. You might find the head drop to 190 or so and the suction real low. This is sorta from left field but its a nice pm job that should be done every year.

[damedi07]

When is the last time the cond coil has been cleaned? If you have a double coil you'll have to separate the two coils and hose them down good. Then check your hi/low side's again. You might find the head drop to 190 or so and the suction real low. This is sorta from left field but its a nice pm job that should be done every year.


yeah but i dont see how he'd have such a high superheat with a dirty condenser coil....it would be lower than normal most likely, and the suction pressure would be higher also.

[51fitter]

yeah but i dont see how he'd have such a high superheat with a dirty condenser coil....it would be lower than normal most likely, and the suction pressure would be higher also.

I was thinking along the lines of the evap coil was being starved. Maybe the cond wasn't doing enough work and not giving the expansion device a full head of liquid? What it gets, it burns off, the load causes the suction line to be warm. Then the compressor overheats. 77 degrees outside and already up to 240psi? If so what is the head when its 95 out? Guess I had to be differant because everyone was looking for a clog. :D

[nineball]

no one has broken into the lines in the last two years. before that, I don't know what happened. The only other thing I did was to replace a condenser fan. The unit worked for over a year without any problems after that. It makes sense to me that I have a restriction of some sort. could the unit be over loaded with refrigerant? Would this cause a reaction like I am describing? I could recover the refrig. and see how much I have. Stage 2 is working ok, and I am getting cooling until stage 1 quits. then the unit won't keep up with the heat load. I am cooling a copy room with a lot of copiers that put out a lot of heat. Therefore I am cooling year round. In the winter with an economizer. Thanks nwtch

Recovering the refrigerant would be a good learning tool for you on this unit since it is small. And will eliminate any questions about correct refrigerant charge. As mentioned may times by others previously your super heat is definitely high. But do we know if this is a TXV system or orifice type metering device. I'm going to guess that this is an orifice type because you described the pressures rising slowly after start up. Normally you will see crazy superheat on a metering device system that have a large load on them. Im guessing the A/C compressor tripped on high temperature causing the space temp to increase to 80+. When you return to look at it again measure R/A and Supply temps before you turn the compressor on this will give you an idea how much of a load you are dealing with.

I'm with 51fitter your condenser coil is probably plugged or something is up with the condenser fan, recheck your work you mentioned replacing the condenser fan in the past is the fan turning in the correct direction? Get a subcool reading and check your condenser for good air flow, the air should be pushing straight up.. If it is blowing out of the schroud horizontily your coil is plugged. Hopefully its not the split coil condenser because they are a pain to clean.. Keep it simple, sounds like you know the history of this unit and it has been pretty trouble free in the past..

Check that condenser coil first before you do anything! ;)

[airon]

A few more things to check.

At an 80 deg space temp that head pressure is not too far out of line.
that suction pressure is a little low. Doesnt sound like a restriction to me but I cant see it.

Check air temp splits across the evap and across the condenser.

The temp splits will help you in your diagnosis, the condenser air temp most of all. On some older units a 30-40 deg rise over ambient would be good.

On many older units 14-20 deg across the evap.

Checking air temps will guide you in refrigerant pressure temp relationship

Gotta use all the tools. could very well be a plugged condenser as well as......

[nwtch]

I clean the coils in all my units in the spring and fall. I use coil cleaner. Sometimes when the cottonwood seeds start blowing, I clean this particular unit
much more often than that. I've got to tell you that coming onto this website has been very good for me. I have been given a lot of things to think about, and I'm sure this will help me as I spend my time in this business. Thanks to all.
nxtch

[saintmichael36]

If the unit has a TXV check the charge by subcooling

To Determine Liquid Line Sub-Cooling (SC):
1. Take the high side pressure and convert it to temperature using chart or gauge.

2. Then take the temperature of the liquid line as close to the condenser as possible..

3. Take the difference between the above readings. (Saturation Temp – Liquid Line Temp.). Note: liquid line temperature at the evaporator should be within 2 degrees of liquid line temperature at condensing unit. If not, could be a restriction or line set too long.

4. Sub-Cooling with a TXV, should be around 9 to 15-F degrees, always check with the mfg’ers for correct SC

5. Then using the information from Superheat and Sub-Cooling we can have some idea where to look for a problem.
Example:
Suction Line Temp is ------- 60 degrees @ condenser
Gauge Suction Pressure is ------76-psig ---- 45 degrees, Read Gauge Suction Saturation Temperature (SST)
60 degrees – 45 degrees = 15 degree Superheat - Adjust charge to the mfg'ers Super Heat settings

Liquid Pressure is ------------226-psig --------110 degrees, Read Gauge - Liquid Saturation Temperature (LST)
Liquid Line Temp (LLT) is -------------95 degrees
110 degrees – 95 degrees = 15 degree Sub-Cooling - Adjust Refrigerant charge to the mfg'ers SC settings

[pmther78]

Try pulling the fan belt and condenser fan motor wires and run the compressor and see if any spots in the evap area ices up then feel around the liquid manifold of the condenser to see if there is cool spots this will help you see if you have restrictions. Be careful not to run the pressures to high!

Good luck!