Ohio Carrier 2 Stage 3 Ton Unit - Open Loop, CXM Trouble Code 4 - FP-1 Low Temp Coax (Water Side Freon Be

Using a downstream valve to create a back pressure and control flow does reduce noise, as you said.

Engineers/Society, including my Brother, say not to throttle with a ball valve. I've used them to throttle at home and they work fine.
Industrial use with higher pressures and flows is where the wear is an issue when throttling.
In an attempt to reduce noise and possible flow loss due ball valve clogging by particles in the water, I tried a gate valve which was more expensive. The noise was still present but I'm sure the Turbulence improved heat transfer through the Coax/Heat Exchanger. I admit there is no fine control of flow when using a gate valve.

 

Yesterday I traveled to the location of the Carrier 3 Ton Unit to take resistance readings on the Thermistor that provides the FP1 input. I took everything I needed but forgot the Carrier installation & service instructions.

For safety, I opened the breaker to the unit which is in sight of the service panel so there was no need to lock out the breaker or open a disconnect prior to working in the cabinet. I don't believe anyone who owns a multi-meter would take resistance readings on live equipment. I wear plastic lenses in my glasses which I believe provide enough eye safety, so I don't wear safety glasses that are required in industry.

I've seen a lot of electronic sensing devices used in the military and industry, but I've never seen equipment where thermistors and pressure switches have the same size, shape and color. In fact all the monitoring devices in the cabinet appear to be the same.
Was this done on purpose or just a coincidence?

Lesson learned, you need the manual/schematic in order to identify components in a Geothermal Heat Pump by their wire color.
By the way, a pressure switch has 0 resistance when closed and looks exactly like a thermistor in a Geothermal Heat Pump.

I passed up using the ECM fan in my Unit out of fear for reliability of an ECM fan versus the standard motor driven fan. The motor driven fan is very reliable, a replacement is relatively cheap and the motor seldom fails from my experience. I hear the ECM fan is expensive to replace even if you do it yourself, plus there's the electronic control card that can fail. Any experience on ECM fan reliability in the industry?

 

Let's talk about Thermostatic Expansion Valves (TXV) in a Geothermal Unit.
I know of one unit in the 90s that was shipped from the factory with a bad TXV, and it had to be replaced before the unit would work. This is probably rare since a performance "Report Card" is shipped with each unit today.

Would it be true to say that if loop flow & temp parameters are in specification, and the unit Freon shows the proper charge and compressor operation, that the TXV has failed?
How often does a Technician find a bad TXV?
Do Technicians watch for signs of a failed TXV like frost on the lines?

With the TXV being the heart of the system, I was wondering how reliable they are.

I have read that in the Inverter Geothermal Heatpumps the TXV valve has been replaced with a variable controlled valve/orifice and allows the variable speed compressor to function in the system. How reliable are these Variable controlled orifices in Inverter Geothermal Heat Pumps, and how many years of operation are projected compared to a TXV Freon unit?

 

There should have been a wiring diagram in the compartment or on the doors.

 

You're right, the schematic is on the inside of the flip down cover that normally covers the boards in the bottom of the unit. I hadn't arrive at my wire color component identification conclusion yet.

I've never worked on equipment where all the components look alike, so I was in new territory. I'm sometimes slow the first time I encounter a new problem, but I always find my way to identify and fix a problem. You can tell I don't work by the hour, I would starve.

Once I flipped down the cover, I used a light to look into the unit, and thought I identified the Thermistor on the Freeon copper line I remembered from a drawing in the manual . When I found no resistance, I wanted to read the section in the manual to see what the resistance was supposed to be. I decided I would return home, read the manual and check the method for reading the thermistor since I have never read a thermistor before. I'm use to RTDs and Thermocouples for measuring temperatures, so I've never had to trouble shoot a thermistor.

 

Pics attached.

A clip on thermistor is usually buried under insulation but it looks like pic. Some models may have the water side thermistors in a wet well.

High and low pressure cutoff switches don't look like thermistors.
Clip on Thermistor
High or Low pressure cutoff

 

I have no less than 4 of the pressure switches looking me in the face when I open the lower cabinet door. Due to their locations, I figured the pressure switches and thermistors looked alike.

The thermistors in your pictures could be buried under insulation and not be visible. I'll use the wire color and connector location as a starting point to find the water side thermistor.

Thanks for the pictures, and clearing up the component identification issue for me geoxne.

 

The print will have colors typed next to the wires. Look harder at what is there.

I am leaving for Mexico if the Donald wins, so call me soon.

I could have fixed this for you way back when.

Mark

 

What if Billiary wins?

 

Thanks for the past help All.
I took the FP1 Thermistor resistance reading today and it was working correctly. The well water was 55 degrees with the unit shutdown, and the Thermistor Resistance-Temperature curve was as close to 55 degrees as can be read on a small graph. I was looking for a temperature closer to 30 degrees to indicate an out of calibration/bad thermistor which would cause a bogus FP-1 set point value of 30 degrees.
The Unit is working fine in Stage 1 (Y1) so I'm going to wait until spring and do a Water Side Heat Exchanger flush, then hook up the Y2 lead from the thermostat.
I believe the Unit will work fine after the mud film is removed from inside of the HX and an Auto Flush filter is installed to reduce mud/contaminate build up.

 

At least I know how Billery thinks.

Does the Donald?

Why is this system beating you up?