Pool Heat Pump Kalos Meeting w/ Bert

Heat pump pool heaters operate on a refrigeration circuit, just like A/C units. They work like normal A/C heat pumps running in heat mode. Inside your pool heater, you have a heat exchanger with water coming in and going out. There are also two copper lines going in.

Superheated, cool refrigerant gas goes into the compressor. After it’s compressed, it goes through the heat exchanger and heats the water. The heat rejection to the water causes the refrigerant to desuperheat and liquefy. Then, it goes through the liquid line (½”, not ⅜”) and into the TXV. After the TXV, the cool liquid refrigerant goes into the evaporator, where the cycle continues afterward.

As with A/C systems, TXV replacement is a common issue on pool heat pumps.

Every pool heater has a heat exchanger. Some heat exchangers have water hookups going in and out with refrigerant lines running within. Regardless of the form, heat exchangers all have the same function: to reject heat to the water and act as a condensing unit.

Heat exchangers can crack and leak water. In those cases, you can expect the culprit to be severe versions of water flow issues, high pressure, the safeties malfunctioning, or high-temperature conditions. Water can only get into the copper lines through a heat exchanger crack (with blown-out copper). However, heat exchangers are pretty durable, so cracks are rare problems.

When heat exchanger cracks do happen, the repair project is usually very labor-intensive. You may be better off quoting for the entire heater. If you quote only the heat exchanger, you will want to test the entire system; you will want to find out what happened to cause the heat exchanger to crack.

Pool heaters also have thermostats, thermostat probes, water temperature, and pressure switches. Water pressure switches are very similar to float switches in their wiring; if 24v comes in and 24v goes out, the heater will know that it’s okay to run. If there is a flow issue that prevents the heater from running, you will see an error code like LO or FLO. Some older heaters may have float switches and pressure switches in the same circuit, and you can figure out if something’s wrong because the pressure switch can open and kill the power. You can ohm the components out with the power off. Clogged filters can also trip pressure switches. (You will also want to install pressure switches after the filter.)

You’ll likely be replacing low and high-pressure switches more often on pool heat pumps than normal A/C heat pumps. It’s also poor practice to quote a switch without finding the issue that caused it to open. R-22 switches and R-410A switches have different pressure limits, so you will want to make sure you read the pressure ratings on the switches.

When you have a pressure issue on a pool heater, it should NOT be your first instinct to add refrigerant right away. Pressure can fluctuate a lot with temperature differences between the pool and spa, and pool heaters tend to be sensitive to refrigerant charge levels. Try to find out why your pressures are high or low; if your pool temperature is cool but you have high pressures, then the pool heater might be overcharged.

A heater will have two thermostats: one for water, one for defrost. The only defrost function is to shut the compressor down but leave the fan on when enough ice builds up. Defrosts tend to be quite long and inefficient, and pool heat pumps don’t generally work very well in ambient conditions below 50 degrees Fahrenheit.

If you need to check your water temperature split, keep in mind that the bottom of the pool is cooler than the surface. You’ll want to read the temperature as close to the base of the pool as possible.

Also, be sure to check the pump timers. The timers may not be running long enough to heat the pool sufficiently.