This morning, my GeoMax 2 (4-ton) went into lockout again, due to low EWT (error code 4).

I shut the system down to reset it, then turned it back on.  After a couple minutes, I heard the compressors come back on, but the gpm meters on the loops showed ZERO flow.  They usually hit 4 gpm per loop.  There was nothing!

I checked electricity flowing to the Flow Center pumps, and the electric is on.

I managed to get a pressure check on the loop:  80psi and 53 psi.

Then the compressors shut down, unit went into lockout again, and the Emergency Heat came on.

I'm calling my new contractor, but it's Sunday, so I hope he'll do emergencies...this does sound like an emergency, right?

Stuart,
The cost of a Sunday service call may exceed the cost of using aux. heat for the day. Certainly call, but consider waiting 'til tomorrow for techs. visit.
Meanwhile you've done some experimenting with the flow center recently, make sure you have power to pump and listen throug hose for rotation. Also verify water pressure if you can.
J

The hvac guy called me back and he's coming tomorrow (Monday) to check it out. Running on EM heat right now, and have pellet stove on. EM set to 67, with fan on continuous to circulate pellet stove heat in that room throughout the house.

Check wiring again and confirmed 220 v going to both pumps on the flow center. Put my ear to the pumps and I'm pretty sure I can hear them turning.

But gpm flow gauges show ZERO flow and usually I can hear the water going through the system. There's nothing. Thermometers on the manifold indicate no temperature delta.

Pressure on p/t ports when system was off was 59 on both in and out. When compressor activated (but flow didn't work), pressure was out-44, in-71. There's no way there should be a pressure drop of 23 psi across the coil. It should be something like 4 or 5 psi.

Somethin fishy goin on.
What kind of antifreeze do you have?
Are you using one or 2 pumps on flow center?
Joe

Sounds to me that the water in your heatexchanger froze, thus there is now ice blocking any flow. You need to check your antifreeze, your loop temps and your flow through your system. The fact that you have a geomax unit (climatemaster clone) suggests to me that your installer got it at a local supply store. Nothing wrong with it, but a local supply chain in my area carried a brand of antifreeze which claimed 100% glycol, but in the fine print it turned out to be only 60%, with the rest being rust inhibitors etc. Caused exactly the symptoms you were describing. One thing you can do is start your unit in A/C mode, that way you heat up the coil and the ice will thaw. If that gets you flow again, you nailed your diagnosis. Has your installer checked your antifreeze with a refractometer? Was is Cryotek 100? It only contains 60% glycol.

Sounds like a very probable diagnosis doc

Posted By docjenser on 19 Dec 2010 12:30 PM
Sounds to me that the water in your heatexchanger froze, thus there is now ice blocking any flow. You need to check your antifreeze, your loop temps and your flow through your system. The fact that you have a geomax unit (climatemaster clone) suggests to me that your installer got it at a local supply store. Nothing wrong with it, but a local supply chain in my area carried a brand of antifreeze which claimed 100% glycol, but in the fine print it turned out to be only 60%, with the rest being rust inhibitors etc. Caused exactly the symptoms you were describing. One thing you can do is start your unit in A/C mode, that way you heat up the coil and the ice will thaw. If that gets you flow again, you nailed your diagnosis. Has your installer checked your antifreeze with a refractometer? Was is Cryotek 100? It only contains 60% glycol.

Doc, you've asked some great questions...here's what I know.

1.  I *wondered* if the water had frozen in the exchanger, or somewhere in the system.

2.  I'm "nervous" about trying to fix the problem on my own prior to the HVAC guy visiting tomorrow (Monday).  Half of me wants to be sure the system is still exhibiting the problem, the other half wants to try and fix it myself.  The new guy is the kind of guy who isn't really a fan of amateurs messing about on their systems. 

3.  Not sure if the new installer ever checked the antifreeze.  All I know is that it is glycol, that's all.  The original installer never told me what brand antifreeze it was.

I guess if the system was working again properly, he could still check the specific gravity of the water/antifreeze.

Posted By docjenser on 19 Dec 2010 12:30 PM

...turned out to be only 60%, with the rest being rust inhibitors etc.
...
Was it Cryotek 100? It only contains 60% glycol.

Why would anyone use Cryotek 100 in a geo loop? It's specifically
formulated for systems with aluminum heat exchangers.

BTW, "only 60% glycol" doesn't tell you anything about its freeze
protection properties compared to 100% glycol. Unless the other
40% is mostly water, the mixture might provide better protection
than pure glycol. It all depends on the average molecular weight
of the non-glycol ingredients.

BTW2, Hercules Chemical is no fly-by-night outfit; they're a major
chemical manufacturer with serious professional expertise.

BTW3, 71 psi IN with 44 psi OUT is the smoking gun. The
heat exchanger is plugged with ice ...or a dead cat.

Looby

Posted By Looby on 19 Dec 2010 01:51 PM

Posted By docjenser on 19 Dec 2010 12:30 PM

...turned out to be only 60%, with the rest being rust inhibitors etc.
...
Was it Cryotek 100? It only contains 60% glycol.

Why would anyone use Cryotek 100 in a geo loop? It's specifically
formulated for systems with aluminum heat exchangers.

BTW, "only 60% glycol" doesn't tell you anything about its freeze
protection properties compared to 100% glycol. Unless the other
40% is mostly water, the mixture might provide better protection
than pure glycol. It all depends on the average molecular weight
of the non-glycol ingredients.

BTW2, Hercules Chemical is no fly-by-night outfit; they're a major
chemical manufacturer with serious professional expertise.

BTW3, 71 psi IN with 44 psi OUT is the smoking gun. The
heat exchanger is plugged with ice ...or a dead cat.

Looby

I can only speculate here about cyrotek-100 here, since I do not know what was actually used. However, in my experience, this was always the culprit. And I thought this is what this forum is all about, the exchange of experience. I am not saying or not whether it should be used in Geosystems, all I am saying that the systems which were installed by other installers with antifreeze from the local supply house, they did not pay attention to the correct freeze properties. They all thought it was 100% glycol and did a 25% mixture with water, when in reality it turned out to be only a 15% solution. I fixed it many times, for others who could not figure out why the heat exchanger froze up as soon as the load gets more serious, usually right before x-mas.
Pattern are always the same. Heatcontroller unit sold by the local supply house to HVAC installer who is relatively new to geo. Supply house also sells antifreeze. Book says you need 25% of glycol for 15 degrees F protection. So they mix Cyrotek 100, which they think contains 100% glycol, but only has 60%. So no, it is not the fault of the manufacturer although the name ("100") is a bit misleading. The supply house does not understand the different application, they actually do the mixing calculation for those guys, and they are the once who try to push out geo units and get all the HVAC guys to install them. The buck stops with the installer, who is ultimately responsible. Stuart, the freezing always occurs in the source heat exchanger, it is the coldest spot of the system. May be by tomorrow the unit will be thawed, and will run flawless for a few hours, usually until 20 min after the installer, who could not find anything, left. Save your installer a trip and tell him to bring a refractometer. Tell him you want the antifreeze checked. I bet you a buck that your freeze protection is between 22-23 degrees.
So now comes the next pitfall, when they try to fix it. They have to drain out some fluid in order to get some higher concentration antifreeze (glycol) in. So the total amount of glycol in the system gets reduced, including some gallons in the purge cart. So it all needs to be accounted for, since the the "new" cyrotek-100 still only contains 60%, but all the mixing tables are made for 100% glycol
We had 5 cases like that last year, and one this year so far. Same mistake done by different installers. The problem is that that the unit thaws and runs normal for a certain amount of time, only to freeze up again later. Usually it creates 1 to 2 week frustration with the homeowner and then the installer until they call us. Keep us posted.

Certainly wait for the tech tomorrow (oops, today) if you are nervous, but I'm betting 5 minutes in cooling mode fixes it (for awhile) Not having prior experience with frozen heat exchangers I'd be nervous about the freeze rupturing it, but Doc makes it all sound routine and easily fixed without long term consequences.

Doc - great stories. Is there any way to verify freeze protection? Somewhere in my automotive toolbox is a $5 anti-freeze tester which works off the density of the coolant - a plastic arrow immersed in the coolant floats up to indicate the freeze protection temperature. If $5 is too pricey, I dimly recall a $2 model wherein one counts the number of colored balls floating and consults a small table.

Surely something similar exists for geo loops...the one I just wrapped up has EWT of 61 in heating mode, so count me out of needing an antifreeze tester.

I never did see a ruptured heat exchanger from freezing, which I find surprising myself. either they are very sturdy, or the pressure goes somewhere. The best way to verify it is to trust your refractometer, not your calculations. The refractometer was always right, the calculations most of the time....
We spend about $150 for the refractometer, ...and then we switched over to Methanol, for all the reasons discussed here before. Happy with the switch, but it is more difficult to accurately measure the concentration. So we pay even more attention with the mixing now.

Here's the update after the new HVAC guy visited.  I really like him.  He doesn't mind me poking and monitoring the system myself.

Of course, the system was working NORMALLY when he arrived.  I showed him the pressure readings I took yesterday when it wasn't working and he agreed the coil was probably frozen.  He confirmed that switching the system to A/C for a couple minutes would almost instantly fix that problem if it happened again.  (I know it was pitched on the board, and I appreciate it.  I feel much more confident now hearing it from multiple people (including the one who would actually have to fix my system if I really screwed it up ) about fixing more on my own.

He checked the in/out pressure and, to his (and my surprise), the pressure was now 78 and 72!  Last night it was 38 and 44.  Weird, huh?  System appears to be running normally (except for higher pressure than usual).

He recommended monitoring it for the next week or two, defrosting the coil as needed if the freezing lockout occurs again, and monitoring the pressure and temperature regularly.

He also plans to test the antifreeze mix to make sure it's correct.

Sounds like you have a tech who understands how at least one of the fundamental components of a geo system works.

I can understand your reluctance to perform an admittedly odd act - turning on cooling in December on advice of distant faceless internet advisors with no skin in your game.

Maybe it is OK to repeatedly freeze a heat exchanger but the idea rubs me wrong. I'd keep a very close eye on it to try to avoid the lockout until the freeze protection level is corrected.

I wish I had an explanation for higher pressure, but I don't.

I agree with Curt about not letting it freeze up again.   If the exchanger gets damaged,  the repair cost will be in the thousands.   Antifreeze is cheap.

To check the antifreeze level - a household freezer does the trick!

Could disabling one of the two flow center pumps slowed down the GPM enough to cause this problem? That is, too much heat extracted from the loop fluid in the exchanger?

I hope not.  The first lockout (low EWT) was a few weeks ago when I did have 1 of the pumps disabled.  At the time, I didn't notice if there was flow or not....it might have been a freeze again.  I didn't think to check.  But I did re-enable both pumps then.  (I didn't tell him about that experiment.)

The 2nd lockout was yesterday and again the error code was "4" for "Low EWT".  At 8 PM last night, I tried the system again, and it worked normally, with in/out pressures of 44 and 38.

This morning, it's still humming away normally when the tech shows up, but the pressures are like 78 and 72.

Re checking the antifreeze in the freezer....just take a little bit and stick it in the freezer and see if it freezes?  Like a few ml?  or more?

How many pumps were running when the 2nd lockout occurred?

Both.

Can't explain the pressures either. At least the delta indicates good flow. The household freezer is usually around 0 degrees F, while the correct antifreeze for glycol usually is 25%, which gives you freeze protection until 15 degrees F.

You can monitor the solution in the freezer and stick a thermometer in when you see crystals forming.....to roughly determine the freeze point.

There is no other obvious explanation, with that flow rate, for the freezing then not enough antifreeze.

The bit glycol you have in the system probably will prevent the bursting, the burst protection with glycol is to a much lower degrees than the freeze protection.
To put it into A/C mode will help you to thaw your frozen coil, but then as soon as you turn it on again, it will freeze depending on how much your loop has recovered and how low your EWT is. This time the unit was shut down for a few hours, giving the ground some time to recover, further down into the winter the freeze up will occur within hours.
Test your antifreeze, don't run your unit until you have fixed this.