I have a 5ton Waterfurnace Envision dual stage unit. It has run flawlessly for the past 5 years. This morning I looked at my temperature monitoring system and notice that since 9:30pm last night, my desuperheater was not making hot water (as it turn out, my furnace was running on Aux Heat).

I looked at the system an it appeared that the water flow was blocked inside the unit. I attempted several things and was able to get the blockage freed. I then proceeded to "clean" the coil with a vinegar/water mix pumped through for 2 hours to ensure that the coils were not built up.
 
Upon restarting the system, it ran for a few minutes and shut down, restarted,....and finally I saw a water flow issue.

Once again the water flow was blocked. After about an hour of trying to run water backwards through it, it freed up again, and the temperature readings of the in and out ports seemed to indicated that the coil was blocked with ice.

My incoming water is 55*F or so, with the furnace off, it was coming out as low as 42*F when the blockage freed up, and finally warmed up to 55*F.

There are no other warning lights on the machine?

Any ideas, I was thinking of turning the unit on in AC mode to see what happens? I'm sure that I will need to read the refrigerant levels,....are there things I can do to diagnose, before I get to that?




Thanks, Rob

In addition, there has been no performance decreases or changes in either water in/out delta or in return/supply delta prior to this issue last evening.

How are you measuring your temps? Do you have any tools to check the in and out loop pressure?

Posted By HVAC Service Man on 19 Jan 2012 09:45 PM
How are you measuring your temps? Do you have any tools to check the in and out loop pressure?

I have a temperature measurement system that has temp sensors mounted around my HVAC system. It logs, the plots and stores the data every few minutes. I can get a pressure reading in the morning. The system is an open loop, pump and dump.

Usually this problem is associated with Pump failure, or resrtricted prescreen, or and inadequate refigerat charge (loss of refrigerant). If the pump is working then, the next step would be to insure the the correct Gallons per minute are flowing. If that is an issue refer to your valves, pressure sw and tank. Open Ground loops are known for there water impurities. They have the highest watercoil failure rates. If your EWT is 50 deg. and you have the correct water flow, on a Geo that is 5 Ton 1.5 gallons PER TON PER MINUTE. are required for a open ground water loop. 8 gpm minumin for this Geo. IF you use this same water source for domestic, then you should be closer to 10 to 12 Gallons per min. IF gallons per min, are good. Then it's time for guages.

Incoming water temps above 50* require 1.5 GPM/ton, below 50* require 2 GPM/ton.

Bergy

When it is free flowing, I have more than 8gpm on my flow meter. What should I expect to happen if I switch it into cooling mode? If I am low on refrigerant, what should happen? I want to diagnose as much as I can before I call a tech out (rural area). Thanks, Rob

Its always a chicken or egg question- is the flow restricted due to icing or is unit icing due to restricted flow. My first move would be to divert drain to sump or elsewhere to establish drain is not plugged.