Delaware high head pressure lock out

So I installed a loop field and am having a hard time convincing the hvac guy that high head pressure lock out is not the loops fault. I was there a year ago and the systems flow rates were confirmed via the 1-800 tech support line. Now the customer is pissed and the sales guy...... for the units claims that the flow rate is not enough. I am heading out in the am to meet the tech and take some readings. What else could be the issue?
Eric

 

What mode of operation? Cooling or heating? I'm guessing cooling?

 

You are correct sir. the system is over a year old and the owner complained of poor cooling capacity right from the start. That problem has been ongoing. The high pressure lock out on 1 unit only out of 2 is new this year. My common sense meter, barring any data collection this a.m. tells me that it is not the flow rate.
I will update later today after call.
Eric

 

So what is the flow rate? Capacity issues are NOT an issue of flow rate....
Edit: I meant to say NOT. Typo!

 

Doc:

Why are you being so short with Eric? He never helped you? He said PM and when you typed it was only before noon. Yet you DEMAND an answer that meets your desired skill level?

I am glad that I will never work for such a nice man as you are.

I am so sorry, I did not mean to type to you as it feeds a troll.

 

Mark,

I did ask Eric a question to clarify things, I did not demand an answer. I had a typo and missed a word.
And weren't you the one arguing lengthily just recently at another thread (Maurice) that a lacking capacity was due to loop issues (air in the loop, lack of flow), and not refrigerant circuit issues?
The rest of your cynicism speaks for itself.

 

As typical with this kind of scenario... No one had the install book to get the pressure drop chart for gpm through the coil. Worse than that the units had been disabled prior to my arrival. so I could not check pressure drop on old flow center. So I changed the single pump flow center to a double as requested and measured a 10 psi pressure drop accrossed the coil. I am working with a carrier 2 ton and 3 ton cube, both 2 stage. I rechecked my math for the single pump prior to going out to the job and all was fine. I also ran it through the Geo-flow calculator and again came up good. I doubt that there is a flow issue with the double or single.

The units would go out on high head pressure after 1 hour of runtime. I was pressed for time yesterday and could not wait for results. I tried calling the HVAC late in the afternoon for results and got no answer. I would have to assume the results with the double pump were the same as the single. or he would have called and been happy the bigger flow center solved his problem.

As I said before the system is 1 year old. Units both ran fine on 1 pump flow center, but customer complained about lack of cooling. The lock out issue is new, and I have to also assume that the lack of cooling capacity is still an issue. I know how to chase a capacity issue, but not a high head pressure lock out.

So back to my original querry. What causes a high head pressure lock out, if we rule out flow through the coil?

 

I've seen paired heat pumps interfere with one another enough to cause lockouts. So plumbing layout can be an issue.

Otherwise, high pressure cooling faults:
- over charged system (refrigerant)
- low water flow
- high indoor air temp
- restricted TXV
- scaled coil

 

thanx Chris.

I installed the flow center with throttling valves so the flow can be balanced for both cubes during operation. If the HVAC lets me back in the loop(pun intended)I will share your list with the tech to make sure he has checked them. I did not really care for management, but the tech was a stand up pro who was only interested in the performance and stopping the service calls.
Eric

 

What is the EWT and LWT on each unit? If the EWT and delta T across the coil is within spec, that should tell whether or not the loop flow is adequate.

What make/model of unit? Has refrigerant ever been added to the unit? When was it manufactured? Several years ago there were widespread problems with sticking TXVs in units with Copeland scroll compressors due to a rust inhibitor used that reacted with the refrigerant oil.

 

I did not hang around due to time constraints. If I get the call back I will gather the EWT and LWT as well as find the book for pressure drop. Is the carrier line built by CM?
Eric

 

Climatemaster used to make Carrier units, but now they are made by Bosch / Florida Heat Pump. If the cabinet has mitered corners, then it is manufactured by Bosch.

 

Eric:

Could there be things growing in the water?

 

I got a lot of conflicting info from the hvac. so when I removed the single pump flow center I opened it up. Clean as a whistle and bench tested fine as well. I am convinced that their is a demon loose on the unit side. I will wait to talk to the hvac on Monday. Part of my visit was predicated on if this fixes your problem no charge. If the issue still exists after the flowcenter change out, I am going to bill. The machines do have mitred corners and I am putting in a call to Jearsey to get a Bosch big book.
Eric

 

I am thinking of little things growing in the system. Stuff large enough to plug a co-ax heat-x, but to small to see if you had a glass jar full of them.

Is there an in-line strainer?

Has the water been treated?

 

Eric, 10 psi is a very high pressure drop indicating a very high flow. Too high for my taste.

We simply need the delta T and delta P for the source side for each heat pump to determine the flow. CM had numerous problems with TXV valves secondary to coil coatings loosened up and plugged the valves. That could trigger your high pressure lockout. Scaled coil is closed to impossible in a closed system, you would pick that up with a high delta T.

If your rest rejection is normal, it comes down to your refrigerant circuit. Either too much refrigerant (unlikely after 1 year of good operation) or an issue with the TXV.

 

High delta P is low flow. Something is slowing the flow.

Mark

 

Yes, the pressure drop in the heat exchanger at a high flow rate is creating a flow resistance.
High delta P indicates high flow.
Unless in the very unlikely event that the heat exchanger is plugged (very unlikely in a closed system), for example with ice (possible in heating mode, impossible in AC mode).
Eric, check the delta T, calculate the heat of rejection. You know within 2 minutes if it is the refrigerant circuit, something else is going on.

The guys at tech support from the manufacturers play that game every time: "oh you flow is off by 1-2 gpm, fix that first and call us back then...". Lower flow increases your delta T slightly , but your flow must be more than 50% impacted to make the heat pump unhappy, depending a bit on the EWT.

 

Doc,
All that has been my experience in the past. Yes the flow is way to high at the hvac guys request, I just did not have the book to verify. Will keep everyone posted as the solution/diagnosis unfolds.
Eric

 

If the unit was employed for heating, low flow is much more likely to cause FP or LP lockouts in my neck of the woods. Biggest problem around here is these funny bumper season days that have 40F nights and 75F days. We get a lot of low coil temp lockouts because usually only one or two sunny side rooms get warm and the others blend are still full of chilly air.