Hello forum, 1st post here. I have a 13 yr old WF 5ton Synergy3 that locks out intermittantly on "water flow". Am unable to solve this daily occurence, as haven't been able to catch it red-handed. Of course it runs perfectly while I'm monitoring it...even tried switching modes backwards and forwards from hydronic to forced-air suspecting a possible faulty diverter valve. Is there an easy way to check the DV valve for bypass leakage? The closed-loop flow is good (15gal/min) with 16% methanol and 39degF entering temp, maintaining a steady delta T of 7.2F. The R22 suction is 42psi and 215psi discharge. I had a tech come by and evacuate the R22, weigh it, coming up only 2ozs light. So no leak. Our local tech has now moved on and our remote location forces self-reliance. Is anybody able to offer further troubleshooting tips? Thanks in advance.

Is there a possible air bubble in the loop? I am just brainstorming out loud here, but in theory if you had a bubble water locked somewhere by the sensor it could show you are not getting enough flow. Have you had the loop flushed recently?

What pressures are you seeing on the loop not just the refrigerant. Your loop maybe loosing or gaining pressure. We had a WaterFurnace envision system that has this same fault and we found the loop would drop in temp so quickly it would loose pressure and cause the waterflow issue but it would not shut the unit down, it would just warn of a low water flow.

You might be able to add a 1 gallon HDPE pressure battery/bladder to help regulate the pressure but you normally don't have this issue unless the loop is dropping in temperature fast and with 39 degree incoming water temps being fairly stable I don't think this is the issue.

Thanks for the reply SkyHeating.

There is a 2.1gal bladder tank installed, showing 20psi.

This heat pump is one of three on the same vertical loop field. The field was flushed and extra methanol added when the problem first surfaced a year ago. Didn't help.
The other two heat pumps have run problem free all along. Each heat pump has it's own secondary circulator in addition to the two primary circulators of the borehole field.
Replaced the problem heat pump's secondary circulator, just incase getting weak, as was 13 years old. Didn't help either...

Is it possible the freeze protection sensor is on the glitch? How to test?

Thanks in advance, John

On newer Envisions, the freeze protection sensor is on the refrigerant line leaving the "water" side heat exchanger. I don't know how the older Synergies are set up but the arrangement makes sense since a freeze can stop all water movement through the system whereas refrigerant will keep moving, so the sensor has a better chance of "seeing" the low temperature condition.

Though it is very difficult to troubleshoot from afar, the one thing that jumped out at me was low side refrigerant pressure - 42 psig. While that MAY be normal, the corresponding saturation temperature (temperature at which the R22 boils at that pressure) is 19*F. That's chilly, perhaps too near the freeze sensor's trip point, typically 15*F or so. Stated another way, the R22 is boiling at a full 20*F below EWT.

If the freeze protection sensor is a typical 10k Ohm thermistor, it is easy to test. All you need is a decent multimeter. The thermistor, when disconnected from the circuit board, should exhibit 10k ohms resistance at 77*F. You can download a chart of expected resistance at other temperatures and check it at other points. 32*F is easy to create with a cup of iced water.

If the sensor is OK, consider these:

1) Low charge...though you had the charge weighed back in (good move), a slow leak may have let enough out to cause the condition
2) Low water flow, but 7.2*F delta-T suggests flow is OK
3) Defective or mis-adjusted metering device - a superheat measurement would help eliminate this. It is easy to measure, but tech needs to know role of heat exchangers in system - where to measure superheat.
4) Fouled heat exchanger - scale acts as insulation, and will queer normal method of inferring flow from water side pressure delta.

Posted By engineer on 12 Feb 2013 08:14 AM
... freeze protection sensor is on the refrigerant line leaving the "water" side heat exchanger.
 
... the arrangement makes sense since a freeze can stop all water movement through the system whereas refrigerant will keep moving, so the sensor has a better chance of "seeing" the low temperature condition.

... low side refrigerant pressure - 42 psig. While that MAY be normal, the corresponding saturation temperature (temperature at which the R22 boils at that pressure) is 19*F. That's chilly, perhaps too near the freeze sensor's trip point, typically 15*F or so. Stated another way, the R22 is boiling at a full 20*F below EWT.

If the freeze protection sensor is a typical 10k Ohm thermistor, it is easy to test. All you need is a decent multimeter. The thermistor, when disconnected from the circuit board, should exhibit 10k ohms resistance at 77*F. You can download a chart of expected resistance at other temperatures and check it at other points. 32*F is easy to create with a cup of iced water.

...

Curt, I always learn a lot from your technical 'how does it work' postings.  Thanks!

I believe the freeze sensor is located on the refrigerant line between the TXV valve and the loop-water-to-refrigerant heat exchanger.

Best regards,

Bill

Bill,

Thanks - my posts generally make sense to me, but not always to others. I'm glad that one was a fair ball.

A sensor located between the TXV and the loop water heat exchanger will experience the coldest refrigerant temps in the system - right where the liquid sprays through the metering device and some of it flashes to gas, long before any superheat joins the party. That makes sense from a freeze protection viewpoint - act upon the lowest temperature present anywhere.

During the first few minutes of a run cycle, pressures and temps may dip a bit below steady state. The compressor will pull the low side pressure down below steady state pressures, driving up superheat, and the TXV will dump some cooler than normal liquid into the evaporator, depressing temps long enough to trip the "Low Flow" (actually low temp) sensor, even though a delay is baked into the logic.

It would be interesting to learn when the charge weight was confirmed and if this system is operating at proper superheat. Many TXVs can be adjusted.

I hope Johman stays with us on this.

Hi Again,

Thanks for the input. Bill is right, your post is very educational...

I found the sensor on the electrical schematic diagram, so followed the yellow wires from the control board to it's placement. How do they expect you to access it? It is totally tucked away under everything with no way of getting at it without cutting a hole in the cabinet sidewall. In order to access it from the front of the case, both the RV and DV valves would have to be removed.
I'm working out of town for a bit now but when I return, will check the resistance. Not sure how those yellow wires are removed from the control board so think it might be easiest to just cut and rejoin them after resistance testing.

Cheers, John

just a swag, but I would also like to know superheat and sub cool. It sounds to me like a TXV.

Sensors are often clipped to tubes, so can be unclipped after insulation is removed - it shouldn't be as hard as it seems. Yellow is consistent with thermistor sensors, so that is a promising sign

Most sensors plug into control boards, so hold off on cutting wires