I've installed a CM 3ton Water to Water that keeps faulting on an FP4 fault code. This fault is low refrigerant temperature. This fault is caused by low flow, faulty temp probes. I first thought the problem to a flow issue due to the filter screen having silt in it. Since then a Sandmaster filter has been installed and the problem is becoming more frequent. The pump is an SQE 3/4 HP Grundfos in a standing column well. The depth is 250 feet, pump at 225, return line at 75 feet. The differential on the incoming coil is 6 PSID which indicates 9 GPM. The system has a Hays 9GPM flow valve. Has anyone experienced this problem before. I think the TXV is malfunctioning. I'm looking for input on an FP4 fault on a standing column well in Maine.

Has a tech checked refrigerant charge?

The refrigerant charge has not been checked. This would require removing all refrigerant then installing new refrigerant and ensuring the proper charge is installed, correct?

No.

A competent tech can measure superheat, subcooling, rates of heat transfers, compressor current, air and waterside flows and delta-Ts, and then calculate actual vs design unit performance as well as whether system is properly charged.

Complete evacuation and then weighing proper charge back in is a sure way of assuring correct charge, but it may not be necessary.

Differential pressure gauges can be decieving, I would first test by discharging water into a bucket and using a stop watch to verify. I would also like a water entering/leaving temp to verify you have adequate bleed off.
Then charge tests that engineer suggests.
Good Luck,
Joe

Joe, just so I understand, what you are suggesting is to divert the water returning to the SCW into a bucket for a stopwatch flow check? If that is easy to do and dumping into a bucket results in same flow as returning to well then I agree...is it possible that return to well encounters back pressure that dumping to a bucket will mask?

I thought Delta-P across a heat exchanger is fairly reliable, but you question that...is that on account of the fact that a fouled or clogged heat exchanger will exhibit both high delta-P and low flow? In which case Delta-T would provide insight?

Just trying to understand the reasoning behind the advice.

Thanks

It's test gauges I don't trust, not Delta P charts. 6 PSI is just a few notches on a mechanical gauge.
Low flow is the number one reason for this fault which occurs more often with the addition of a new filter.
We put flow gauges on all our open loop systems to help with trouble shooting.
Low EWT (caused by inadequate bleed offr) can make refrigerant pressure low. Low flow can make for higher DT.
Above all else no refrigerant gauges should go on equipment until flow is verified.

Should ask earthheat how long has this heat pump been in service?

j

> is it possible that return to well encounters back pressure that dumping to a bucket will mask?
> a fouled or clogged heat exchanger will exhibit both high delta-P and low flow

Yes and yes.

I have a fairly decent Dwyer 0-60 psi guage I've used a couple times for Delta-P. I've seen folks use a $7, 0-100 psig guage from a big box store and agree that it isn't likely to be accurate over the few pound range of interest to us.

An industrial 2-port Delta-P instrument would be useful on a closed loop, but they aren't cheap, and one has to be certain the sensor can stand the relatively high absolute pressures. Maybe I'll look into a digital 2 port delta-P guage plumbed to a couple of sport ball inflation needles via flexible tubes and isolation valves.

"In which case Delta-T would provide insight?"
Delta T is a piece of the puzzle. If EWT is good LWT water temp too low is going to be flow or refrigerant charge. You shouldn't find a proper LWT when you're tripping on Low pressure.

As problem seems to be intermittant, I'm leaning towards a water problem. Refrigerant problems usually don't cause intermittant lock-outs.
If I had to guess flow is impeded or bleed off is inadequate.

If earthheat is still around: how old is system? How often is it locking out? can you tell us your entering and leaving water temps? Do you clean filter everytime system locks out? We are talking heating not cooling right?
j

Can you hook your system temporarily to your domestic or another water source to rule out refrigerant problems

With a 75' down return line, you have, depending on pressures and valve location, the potential to vaporize water in the HE. Make sure the HE exit maintains some pressure (or dump to a drain for testing).

Posted By jonr on 03 Apr 2010 05:19 PM
With a 75' down return line, you have, depending on pressures and valve location, the potential to vaporize water in the HE. Make sure the HE exit maintains some pressure (or dump to a drain for testing).

Ummm...vaporize, as in boiling water while simultaneously tripping low refrigerant pressure? Or did you mean atomize due to pressure and restriction? What? 
Never mind. Think OP bailed can't get questions answered. Dead thread. 
J

Yes, the former, ie, vaporize the water even though the temperature is low - ie, even cold water boils as pressure approaches zero absolute (which is hard not to happen with 75' of water pulling downward).

Got it. Has this occured often in your field work?
As you are not familiar with heat pumps in operation, you may be interested to know a unit with little or no flow will have a cycle time more easily measured in seconds than minutes.
How do you have any flow of water (it would have to be present to be vaporized) and create that significant a vacuum at the same time? All within the short time it takes to trip on low pressure?
j

You need to get some more education about basic hydraulics. You will then realize that your assumption of little to no flow will not occur - in fact the opposite, the discharge water head acts to increase flow (because it reduces pressure at the HE outlet). Operating hydronic systems with any point at close to zero pressure is a bad idea (most do the opposite and pressurize for related reasons).

I'll take that under advisement. Meanwhile you might want to educate yourself on how geo systems (and for that matter boilers) work (since you present yourself as knowledgable on a geo forum....or at least this one that you haven't been kicked off of yet). No one has disputed water vaporization in a vacuum.
How can I speak (or type) slowly enough for you to understand your pet uncommon occurance of the day could not possibly damage a geo system that will lock out in the absence of flow?
You muddy waters of threads, authored by people who have legitimate problems, with wild @s$ theories.
I ask questions to help.
J

> How can I speak (or type) slowly enough for you to understand ... could not possibly damage a geo system

Great, another straw man argument (and more condescension). Of course nobody mentioned damage.

Perhaps education on stating opinions without being condescending is in order.

Absolutely - starting at post 04 Apr 2010 10:59 PM and progressively getting worse in 06 Apr 2010 09:55 AM and 07 Apr 2010 12:07 AM.