Compressor has high head pressure immediately after startup

[crashputer]

Hello,

I hope I am posting this in the correct category. I operate a chiller at an outdoor ice skating rink. The system is seven years old and has operated fairly well in that time.

Over the past few weeks it would have an occasional shutdown due to high head pressure. I called my local technician to help with this problem, and we came to a solution that seemed to work well. However, over the last weekend one of my compressors shut down due to high head pressure, and now will not run for more than a few seconds (5-10) before shutting down again.

At first I suspected a faulty pressure sensor, but we checked the pressure with gauges, and the gas side of the compressor spikes wildly and never settles. We checked all the valves in the system and everything appears to be functioning normally. The condenser fans are running normally and all system voltages are normal. That being said, it is entirely possible we have overlooked something.

Having exhausted all other ideas we set the superheat controller to hold the expansion valve at 10% for 30 seconds during startup (normally set to 50% for 5 seconds). As expected the pressure drops until the valve opens. Then it rises fairly quickly until emergency shutdown (< 30 seconds). At this point we have run out of ideas.

My setup:

Bitzer 6F50 compressor
Emerson ECE-X33 superheat control system, EX6 valve
CAREL pCO3 PLC
R-507 refrigerant

[NiHaoMike]

Assuming no unauthorized service has been done, make sure the condenser is clean.

[Nuclrchiller]

Also, make sure that a free wheeling condenser fan, rotating backwards, hasn't been mistaken as running normally. I've seen that mistake made more than once. Even by people who should know better...

[union 189]

Check expansion valve for proper operation

[crashputer]

Thank you for the responses.

The condenser is clean and clear. I thought perhaps ice had formed inside the cabinet due to recent cold weather, but I checked and it is clear.

The fans are operating normally and spinning the right direction. I had a person manually engage the fans while I was near to check for slipping/other issues, and they are both operating well and spinning the right direction. The cabinet itself is sealed and closed (it's a walk-in style condenser cabinet).

As a test I manually engaged both the primary and secondary fans before starting up (the secondary fan is set to engage at 280 pounds pressure (my technician's recommended pressure)) and still had high pressure.

The expansion valve appears to be operating normally. I normally have it set to the factory setting of 50% at startup for 5 seconds before switching to automatic mode, but while diagnosing this problem I have it set to 10% for 30 seconds. I can hear it moving after switching to automatic, and there is a lot of hunting. All four of my units do that for a minute or so at startup before stabilizing. This unit does not have a chance to stabilize before shutdown.

I would suspect an overcharge of refrigerant, but we have not added any refrigerant or oil in five years, and the system has run well until now.

Just for the record:

This unit is used seasonally from November through March. It is offline from April through October. We take oil samples each year before startup for testing. I check oil levels about once every two weeks and perform other routine maintenance on the manufacturer's recommended schedule. Any repairs or maintenance that affect the operation of the compressor units and their related parts is done only by our certified technician. In this situation even he is stumped.

[KnewYork]

Is this a dual circuited unit? If so, what is happening with the other compressor? I have seen (on many occasions) where the refrigerant from one circuit made it's way into the other circuit through faulty gaskets. One compressor would go off on high discharge pressure and the other would cycle on low refrigerant pressure.

[jayguy]

What is the High Pressure Cutout Setpoint?

[crashputer]

The cutout point is normally set to 350 lbs. My technician had me raise the point to 400 lbs temporarily, just to see if it would cough up a hairball and stabilize. I will not be leaving it there once this situation is resolved.

[crashputer]

These are four isolated circuits. The only point of contact is in the chiller barrel, and even then they have independent pipes. I have not noticed any changes in the other three cabinets.

I'm glad they're independent, actually. At the beginning of this season I had a burnout in the #3 cabinet (bad power phase + faulty overload sensor = bad things), and the repairs would have been exponentially higher if they were dual-circuited.

[jayguy]

So, did you ever check the %RLA at start up to see if it is starting loaded?

[emcontrols]

When you refer to % EXV is that 10% open or 90% open, and when you release control it closes or is there another electric valve you are referring to IE Hot gas bypass or unloader etc. And what superheat are you actually running compared to what the controller is trying to maintain. Could simply be a faulty saturated suction temp sensor thinking the evap is flooded. Need to check sensor with actual measured. The more info the better, like what exactly are you working on M# manufacture, possibly a log sheet. Just my two cents worth.

[KnewYork]

The only point of contact is in the chiller barrel, and even then they have independent pipes.

True, but what separates the circuits are gaskets...the only thing separating the refrigerant circuits from each other. If the gaskets fail then the circuits can "swap" refrigerant.

[crashputer]

True, but what separates the circuits are gaskets...the only thing separating the refrigerant circuits from each other. If the gaskets fail then the circuits can "swap" refrigerant.

Hmm... I haven't had any noticeable drop in pressure in the other compressors, but while checking all systems the other day I noticed that the pressures on them were topping out around 250. I wasn't overly-concerned because the ambient temperature was low. However, last year I had to add refrigerant to two of the compressors, and my technician spent a long time with his leak detector and was unable to find anything. I'll investigate this a little more. This repair sounds like it's needlessly complicated?

[crashputer]

Also related: The installer of the ice rink did not calculate head or size the brine pumps appropriately. The chiller barrel is designed for a maximum of 700 gallons per minute flow. The pumps were pushing nearly 1200 gpm. I corrected this problem with a variable frequency drive, and now run slightly below 700 gpm. Could this have damaged the gaskets or is the brine chamber isolated from the refrigerant lines?

[teddy bear]

If you trap air in the condenser, the air is uncondensable and will show high head. With high head from the refrigerant, you will have high heat. Trapped air is uncondensible and will have a hot condenser. Shut the system down and bled at the compressor discharge. This will bled the trapped air. Any leaks on the low side could suck air into the system is the low side is negative.
Regards TB

[KnewYork]

Also related: The installer of the ice rink did not calculate head or size the brine pumps appropriately. The chiller barrel is designed for a maximum of 700 gallons per minute flow. The pumps were pushing nearly 1200 gpm. I corrected this problem with a variable frequency drive, and now run slightly below 700 gpm. Could this have damaged the gaskets or is the brine chamber isolated from the refrigerant lines?

They are separate. Yours is a DX chiller where the refrigerant passes through the tubes and the water travels on the outside of the tubes trough a series of baffles.

Fixing the gaskets between circuits is a major PITA.

[KnewYork]

If you trap air in the condenser, the air is uncondensable and will show high head. With high head from the refrigerant, you will have high heat. Trapped air is uncondensible and will have a hot condenser. Shut the system down and bled at the compressor discharge. This will bled the trapped air. Any leaks on the low side could suck air into the system is the low side is negative.
Regards TB

Bleed to atmosphere? Pretty sure that's illegal. The compressor is nowhere near the high point of the system, which is where any non-condensibles would tend to accumulate.

How did the non-condensibles get in there?

[crashputer]

Re: bleeding through the gasket... would there be any chance of introducing brine (in this case, 35% propylene glycol solution) into the refrigerant system? I spoke to a person at my vendor's office (not the technician, he was out of the office, but a person who has dealt with this scenario) and he mentioned the possibility to me. So far I have no evidence of this.

As far as non-condensables in the condenser, would that suddenly from nowhere cause near-immediate overload? And as long as my compressor has been offline, would it not be a detectable refrigerant leak instead of suction?

[TF12]

What saturated suction does the machine operate at? I have 2 06CC Compound reciprocating compressors that use 507 to chill a thermal fluid Syltherm to -57 C. The low side operates in a vacuum even though it is a high pressure HFC refrigerant. Suction normally runs 1-2 inches and the head around 200. We had a king valve pulling air in on the low side causing a similar issue. However if non condensible gases are expected just pull the charge and repair. Do you know if you have a discharge check valve??

[hvactech1977]

sounds like bad txv