In this short episode from the Bry-X stage of the 7th Annual HVACR Training Symposium, Tessa Murry gives a class on building science basics: The House Always Wins! Tessa is a building scientist who works with TEC.

Tessa's class is about how the house puts HVAC contractors in difficult situations. When people have indoor air quality or comfort concerns, the HVAC often takes the blame, even if the issue is with the house. There are usually several little home improvement decisions that create unintended consequences and add up. In many cases, when there aren't exhaust fans in kitchens and bathrooms, moisture stays inside and can cause indoor condensation. Air-sealing, adding or removing insulation, replacing windows, replacing furnaces with a different efficiency model, and even moving people in can all affect comfort and air quality.

Comfort issues and complaints, such as hot and cold spots, often point to issues with the house, not necessarily just the HVAC system. Pressure boundaries and thermal boundaries in the building envelope need to be aligned, continuous, and consistent for HVAC systems to do their job well, but many houses don't have that. Those boundaries need to be clear between attached spaces like attics or garages. Those spaces create problems with energy efficiency and comfort, and humidity is a problem in some climates. Garages also have fumes we want to keep out of the house.

Heat moves from hot to cold, and air moves when there is a pressure differential. Mechanical equipment and wind can drive pressure differentials. If there is a pressure difference and a hole, there will be air movement. In the winter, cold air sinks and displaces warm air, which rises and creates positive pressure at the top of the house. That air will push through gaps around can lights, vents, and more. When that humid air gets into a cold attic, the moisture will condense on the roof decking surface and cause an ice dam to form. In the summer, hot, humid air comes into the structure. Regardless of the house's issues with air movement, it's on HVAC contractors to make the decisions that put the occupant's health and safety first, including calling the contractors with the knowledge to diagnose the house's problem.

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In this short podcast episode, Bryan talks about multi-position service valves and more valve types.

Many typical residential systems have brass service valves with a hex cap and Schrader ports; access happens solely through the Schrader ports (where the cores are). Schraders are restrictive and prone to leaking, and they don't have the ability to back-seat or front-seat. In applications where we need that capability, we use multi-position service valves instead. (Note: CoreMax valves have much higher flow rates, but you can't remove the cores except with a highly specialized tool.)

Multi-position service valves are common in commercial refrigeration and allow for unrestricted, full-port flow. They do not have spring-loaded cores in the service port. If you treat these valves like Schrader valves, refrigerant WILL come out if it's not back-seated. You adjust the position by turning the stem with a refrigeration service wrench; loosen the packing nut before attempting to turn the stem, as tightening it down will crush the compressible packing material around the rotating stem. Tighten it back down after making your adjustment.

These valves also require lots of heat to braze, so we must cover heat-sensitive surfaces with wet rags or heat-blocking putty (like WetRag by Refrigeration Technologies). The valve must be mid-seated while brazing, not fully front-seated or back-seated, as the surfaces are more likely to warp otherwise. Mid-seating the valve also provides a high-volume path directly to the system. Back-seating the valve is the everyday running position (stem must be rotated fully counterclockwise) and blocks access to the service port. Cracking off the back seat requires you to rotate the stem slightly clockwise with service hoses securely attached, just enough to allow you to get a reading through a tiny gap. Front-seating the valve is good for isolation with the compressor off but may cause compressor failure or serious injuries if you run the compressor. Front-seating requires you to rotate the stem fully clockwise; it completely blocks the flow of refrigerant through the system, and the service port stays open to the upstream side of the valve body. Catastrophic compressor failure will happen if the suction or discharge valves are front-seated while running.

General multi-position service valves are NOT king valves. King valves are multi-position service valves specifically located at the outlet of the liquid receiver. These valves front-seat to help you pump down the system when you need to do repairs on the low side; it blocks liquid refrigerant from leaving the tank. A queen valve may be located at the inlet of the receiver on the drop leg from the condenser; front-seating it with the king valve will fully isolate the receiver.

Multi-position service valve tech tip: https://www.hvacrschool.com/compressor-multi-position-service-valves/

Have a question that you want us to answer on the podcast? Submit your questions at https://www.speakpipe.com/hvacschool.

Purchase your tickets or learn more about the 8th Annual HVACR Training Symposium at https://hvacrschool.com/symposium.

Subscribe to our podcast on your iPhone or Android.

Subscribe to our YouTube channel.

Check out our handy calculators here or on the HVAC School Mobile App for Apple and Android.