Opinions wanted

[Ruudacguy]

2000 model Tempstar 10-ton RTU gas pack. Refrigeration system is 2 staged 5 ton systems. 1 stage uses the top half of the condensor coil and 2nd stage uses the bottom half. Theres 2 condensor fan motors which are both running at the same speed all the time.

The problem is 2nd stage cooling has high head pressure and cycles off the HPS. 1st stage pressures were 75 and 300. 2nd stage pressures will climb slowly and within a few minutes the high side climbs to 400 and the HPS will kick the 2nd stage off. The suction climbs to about 85.

The condensor coil is spotless, now. Before I foam-brited it the 2nd stage would cycle after about 20 seconds of runtime. After the cleaning, the 2nd stage would run for about 2 minutes.

I recovered 1 pound of refrigerant yesterday out of the 2nd stage yesterday, just as a temporary fix to get the head pressure down so they could have the 2nd stage running even if it is a limited capacity. Its been in the 90's and this unit is in a bar. I shut the unit down for an hour yesterday to clean the coil and they about ran me off. I got the head pressure down to about 360 steady and the suction dropped to about 70.

My next step is to recover everything out of the 2nd stage and weigh the 9lbs 6ounces back in. This would eliminate the possibility of being overcharged. I would have recovered everything out of the 2nd stage yesterday but all my cylinders were full. But, I'm real sure its not overcharged. I dont think anyone but me has worked on it. And, if someone else did have their gauges on it, I dont see how anyone could have ever diagnosed this unit as being low.

Lets hear it!

Andy

[OkieBill]

Andy,
Ok I will give it a shot:-) though some of these may be far out...

Is this unit on a roof by chance? If so verify the temperature of the air going through the upper and lower part of the condenser may be a difference due to hot roof... ( I have seen this on roofs a few times)

I will assume that there are no airflow issues (obstructions) on the condenser...

First verify proper charge by weight for sure.( you removing a lb. and getting the pressures closer to right tells me that the system is overcharged)

What is the temperature inside the conditioned space when you are observing these pressures...

How is the evaporator set up for these 2 stages ( is the load split evenly)?

What type of staging control is used to cycle these systems ( Pressure switches, Temperature Delta, electronic ect...)

[Ruudacguy]

Andy,
Ok I will give it a shot:-) though some of these may be far out...

Is this unit on a roof by chance? If so verify the temperature of the air going through the upper and lower part of the condenser may be a difference due to hot roof... ( I have seen this on roofs a few times)

This is a packaged RTU, but it is not on a roof. It sits on the side of the building on a 24" curb. That is a good idea though! I can see that happening for sure.

I will assume that there are no airflow issues (obstructions) on the condenser...

I am not happy with how close the return duct is (that runs up the side of the building) in relation to the backside of the coil. But, this unit ran great last year and none of that has changed.

First verify proper charge by weight for sure.( you removing a lb. and getting the pressures closer to right tells me that the system is overcharged)

I had the same thing in mind, Bill. But I worked on this unit last year and it worked great. So much so, one of the nighttime bartenders wanted to thank the hell out of me. I am about 99% sure noone else has touched this unit since last year. Before I worked on it last year, someone had taken a CO2 tank to the condensor coil to try to clean it. They flattened alot of the fins over. I combed it out, cleaned it, charged them, accepted my tip from the bartender, etc...

What is the temperature inside the conditioned space when you are observing these pressures...

About 80. Yesterday evening when I left it had gotten to about 78 after I hacked into the second stage. But, another 50 people had piled in the bar for the hour or so I spent observing. I havent heard today, but I have to think the second stage is partially working.

How is the evaporator set up for these 2 stages ( is the load split evenly)?

Im gonna look at that the next time I am out there. I dont know if its interlaced, stacked or split half and half. Part of the problem is I need to shut this thing down to properly troubleshoot, and I just cant cause its so damn hot.

What type of staging control is used to cycle these systems ( Pressure switches, Temperature Delta, electronic ect...)

Its just a 2 heat 2 cool stat Bill. Im real sure the stat is the only thing that controls the firing rate.

If you have any other ideas I am all ears!

Andy

[OkieBill]

Andy,

Verify the delta of the air going through Stage two of the condenser ( Use cardboard to block stage one part of condenser) Then you should be able to prove or disprove condenser airflow issues...

[NHMaster3015]

Txv?

[jeff]

Does this unit have a split condensor coil out side coil clean inside coil pluged up jeff