Dan Rasmussen, product support team leader, started by focusing on mechanical refrigeration troubleshooting for R-22 and R-410A. Thinking safety first, he talked about R-410A safety and handling.
For R-410A, pressures are 60% to 70% higher than R-22, he noted. Evaporating and condensing temperatures are about the same.
Inhalation of R-410A vapor may cause irritation. “At high concentrations, it can cause asphyxiation. Large leaks require evacuation,” he said.
This refrigerant is combustible under pressure when mixed with air. Avoid exposing it to very high temperatures, he warned. Contact with certain red hot materials may cause an explosive reaction.
When working with R-410A, “You will need a new gauge manifold set and hoses,” Rasmussen told the dealers. It will require up to 800 psig high side and up to 250 psig low side. Hoses must have a service pressure rating of 800 psig. A recovery cylinder must be rated at 400 psig.
R-410A uses polyolester or POE oil. It cannot use mineral oil like R-22. POE oils and moisture will not separate under a vacuum, he stated. “When servicing an R-410A system, the liquid line drier must always be replaced.”
Always evacuate to 500 microns, he said. “Make sure you have a micron gauge and condition yourself to use it.” With it, you can be sure you have a good vacuum.
“Using your refrigeration gauges allows you to convert pressure to saturation temperature,” said Rasmussen. This is the first step in the analysis of the system.
The evaporator coil’s function is to act as a heat transfer surface for the refrigerant. The coil has a metering device that drops the pressure of the refrigerant from high to low. The low-pressure refrigerant leaves the metering device at a saturation temperature corresponding to the suction pressure.
Since the refrigerant is at saturation temperature, the addition of heat causes the liquid to boil off to vapor. When the vapor leaves the evaporator, it will be at a temperature above saturation temperature, which is superheat.
“With changes in outdoor air temperature, the amount of liquid entering the evaporator is constantly changing,” he explained. High outdoor temperature causes high pressure. Low outdoor temperature leads to low pressure.
If the refrigerant charge is too high, the coil will flood and superheat will be low. If the charge is too low, the liquid will boil off quickly and superheat will be very high, causing the compressor to overheat.
The problem of high heat load can be caused by:
Low heat load can be caused by:
R-410A systems use a thermostatic expansion valve to meter the refrigerant. This valve will try to maintain a constant level of superheat. Using a TXV, if heat load is high, superheat will be high. If heat load is low, superheat will be close to normal.
With an overcharge, the TXV may close and maintain superheat and suction pressure. With an undercharge, the system will operate like a fixed metering system.
Low subcooling means the system may be undercharged. High subcooling means the system may be overcharged.
Most systems will perform with about 10Â°F of subcooling. For R-410A, the 10Â° level of subcooling allows for a standard pressure loss of around 50 psig.
High subcooling and liquid pressure indicates a flooded state. Low subcooling and liquid pressure equals a starved state. “The liquid line temperature should never be below ambient temperature,” he said. If it is, you have a restriction.
These dual-compressor units run one compressor at a time. The product is cooling only or heating and cooling heat pump models.
“The small compressor — the first stage — runs and maintains temperature 70% to 80% of the time,” said Stecker. The large compressor runs only when the small compressor can’t handle the load. The dual-compressor model matched with a variable-speed indoor unit provides enhanced airflow, supplying greater humidity control. This feature is called Comfort-R™.
An oil equalizer line between the two compressors maintains proper oil level in both.
First stage airflow is 50% of programmed airflow for the outdoor unit size. Ductwork is sized according to ACCA Manual D standards. “Select registers for acceptable throw at first-stage airflow,” he said.
The system is controlled by a microprocessor in the outdoor unit. Three LEDs indicate system status and are used for troubleshooting.
For heat pump control operation, he pointed out, “The defrost control has more control over decisions on operation than in prior units.” The defrost control microcomputer determines the need for defrost by continuously measuring the difference between ambient and coil temperature.
If a compressor has failed and the system is not acid, he stated, you only have to replace the compressor that failed. If the system is acid, you need to change both compressors.
Additional presentations during the weeklong training included furnaces, variable speed, heat pumps, and duct design/airflow considerations. Attendees were also given a lab tour and a factory tour so they could see American Standard products from birth, up close and personal.
After completing this intensive training, the dealer is ready to take care of his/her customers with a detailed plan because, as the company’s brochure says, “The rest is up to you.”
Publication date: 05/14/2001