I’ve posted this on a few geo-thermal forums. SDMB always amazes me, so here goes:
I have a 1998 Carrier Geo-thermal unit set to 'Cool" on the house thermostat. It is an open-loop system making use of the current house water well.
My t-stat is set to 76 and I am getting cold air. The house is cooling. The indoor temp on the t-stat is 78. These numbers are important.
If I lower the set temp to 74 to cool the house from 78, a red t-stat light will come on and what feels like non-cold air will come out of the registers, and the house temp will creep up to 80…81…82… (outside temps cracked 90 today and evening temps are in 80’s).
Ok… I power the unit OFF via the t-stat… Wait a few plus minutes. Okay, house is, oh…say 80 nbow… and if I set temp to 78 (just two degrees below house temp), I get cold air – Good, real cold air. No light comes on the t-stat.
If I drop the set temp to 75, for example, a red light comes onthe t-stat… air from registers feels room temp and house temp hold at 78 or creeps up again.
I am not the owner who installed this Carrier unit.
Ain’t technology fun?
Is it a Honeywell Vision Pro 8000 touchscreen thermostat? (or similar?)
More questions…
If you left the thermostat alone and continued to get cool air, would it continue to cool correctly down to the 76° you mentioned?
I do not work residential. But my guess from my desk, 2 stage unit low on charge trips out when 2nd stage kicks in. You are going to need a service call.
post the model number of the unit and stat
My guess would be that your AC has multiple systems in it (probably the ground-sink unit and a more conventional one) and that it’s set to use only one of them when it’s close to its set point, but both when it’s far from its set point. Presumably, the second system is malfunctioning somehow such that it’s producing more heat than it’s pumping out. There’s probably not much you can do about it yourself, though, and even less that anyone can help you with over the Internet.
I’ll throw in 2 cents.
Disclaimer: I am not playing expert and am not claiming to be able to diagnose your problem from the information provided.
However, I do a have a geothermal heating/cooling system in my house. My electric bills spiked horribly this winter but it was a very cold winter and I have not had the system long enough to really know what the baseline was.
I had the system serviced this spring and found out that one of the zones had a coolant leak. I had been heating one zone of the house on the electrical backup system which draws heavily on electricity. There is no oil or gas heater.
What I’m getting at is that maybe your system has leaked it’s coolant and is running on backup. Get a qualified technician in there immediately to check it out. Whatever you have to pay for the service call will be gained back in energy savings. They have the tools to check this stuff out. Also, there may be something like a 10 year warranty on the system (if you are lucky) and any replacement parts will be covered.
Good luck!
Is there an “L” terminal on your stat?
Is there a “Y2” terminal on your stat?
Are there wires on those terminals?
Darn, I meant to answer these questions when I was home so I could report back on model numbers of everything from T-stat to the unit itself and other details. I am at work now.
Here is what I can add: It had a coolant leak that was obvious over the winter, so a dye test was done and the coil showed a leak. No other leaks were visible. A coil was ordered and installed and we were back to lower bills and mostly the benefits of geothermal power (the emergency electric back up heat went off and stayed off).
This is a two stage system. It has two compressors. Clearly, one is kicking out cold, artic blast air, and when stage 2 comes into play, that cold air goes away and ever-so-slightly cool air comes out.
It runs very cold when maintaining a temp, too. It will back down to a very low fan speed setting and a trace of very cold air will flow thru the evening.
I will do my homework and answer all questions this evening. I will place a service call, but like to be armed with information. Sounds like there is chance the compressor for stage 2 is shot. I though there was one common coolant for both stages… from going over the unit with a pro back when I was getting the coil replaced. Maybe I am misguided here… ? Does each stage have it’s own coolant?
.
UPDATE: Both stages are kicking on as intended. Stage one does seem colder than when stage two is on. Coolant is charged properly and has been in both stages.
At the breaker panel, I have disabled the emergency/electric heat (in case the t-stat was throwing on the emergency heat).
The air is only slightly cold.
In summer/cool mode, I know that there is some reversing valve and/or process that has to take place. Where I think I should focus is on whether this is working properly (wonders?). I mean, compressors work, they have coolant and yet the air is not very cold at all. In winter, they pumped up the heat just fine. They were able to keep the house at 68 when it was 25. Now, in summer… If it is above 90, I can’t get the house below 81.
Air filter = new. Returns, registers, etc all free and clear. Air flow rate is normal.
I know my GeoT unit heats the hot water somewhat, too. But how is the rest of the heat carried away? Is it possible I am getting some heating action countering cooling action? Again, these are the same compressors kicking in that will pump out the heat and make a cold house warm, but now can’t make a hot house even temperate.
?