THE HARD START & POTENTIAL RELAY

I have spent most of my career being afraid of hard start kits, I heard too many horror stories of start caps exploding and sales technicians telling every customer they need one.

It dawned on me recently that it may be time for me to take a more mature look at start capacitors, potential relays and hard start kits and find some best practices.

Let’s start with how they work.

When a compressor first starts up, it requires a lot of torque to get from 0% up to 75% of running speed, especially when it has to start under pressure load (unequalized pressures). A start capacitor is designed to create the optimal phase shift for that first 75% of synchronous speed. A run capacitor is sized to create an optimal phase shift for a compressor that is running at full speed and at full design load because the run capacitor never comes out of the circuit.

While a run capacitor has heat dissipation capability for constant duty a start capacitor MUST be taken out of the circuit VERY quickly to avoid melting down as well as causing compressor damage.

The start capacitor is REMOVED from the circuit by a relay called the potential relay. The potential relay is normally closed and it OPENS when a sufficient PICKUP voltage is present between the 5 and 2 terminals on the relay. This pickup voltage is potential (voltage) that exists in the start winding when a motor gets above about 75% running speed and it is GENERATED in the start winding by the motor itself NOT the capacitor. A capacitor DOES NOT boost the voltage, when you see that increased voltage across the capacitor that is back EMF being generated by the motor, just like in a generator (pretty cool huh?).

Some hard start manufactures wire the coil on the potential between start and common and some wire it between start and run. You will find that most OEM’s wire between start and common but this does not mean that wiring between start and run is bad… it just needs to be designed correctly for that purpose (Kickstart does it this way for example).

A properly sized start capacitor and potential relay are not BAD for a compressor, they just must be sized and installed correctly and there are some cases where they are more likely to be useful that others.

Cases where they may be very useful useful

  • Long line set applications
  • Hard shut off valves
  • More often on reciprocating compressors than scroll or rotary (but still OK on scroll and rotary when beneficial)
  • on 208V single phase applications

Things to consider

  • Mount the relay properly, there is a proper UP configuration on most potential relays
  • Use hard starts with REAL potential relays not timers, solid state or other relay types (in my experience)
  • Size the relay and capacitor according to manufacturers specs
  • Ensure that you have a good quality, properly sized run capacitor on any system with a hard start

For a complete write up on potential relays you can read these articles HERE and HERE

source: hvacrschool.com

17 Mar

Is it possible to prevent smoke coming into the house and how much would it cost?

Findingmorty asks:

My neighbors smoke like fiends and I’m having breathing difficulties. As best as I can tell, they smoke outside and it drifts up and into the attic via a permanent vent on the side of the attic. Then somehow it makes it’s way into my room and the ventilation system. The A/C unit is on top of the house and come summer it will suck it in as well and blow it all throughout the house. Is there anything an HVAC professional can do about this and how much would it cost?

Can this issue be fixed? Yes, Will it be expensive? Yes. Your house is allowing outdoor air, which is contaminated with things such as your neighbors smoke, because your home is under a negative pressure and/or extremely leaky. The first thing I would do is find a reputable HVAC contractor who specializes in indoor air quality. They can examine your homes envelope and HVAC duct system and other venting systems like bathroom and stove exhaust to try to determine exactly how the smoke is making it into your living space. From there they should be able to recommend steps that can be taken to correct the home envelope. Another benefit to hiring a professional such as this is that many of the repairs needed to solve problems such this also benefit you by preventing the outdoor heat from entering your space in the summer which in turn can dramatically lower your electric bill. A less expensive option may be to purchase either a duct mounted whole home PCO type of air purifier or a standalone one. You will need one that either has an ionizer or PCO (Photocatalytic Oxidation) technology. Keep in mind that ionization will produce ozone so for some people can cause issues, however it is very good at getting rid of cigarette smoke. I hope this helps.

James Bowman, National Technical Manager, HVACR

13 Mar

Eliminate Drain Stink-Bugs and Trap Primers

Rick Ensley will be conducting a QuickFire Session at the NFMT 2017 March 9 in Baltimore

Join leading equipment and service providers like Rick Ensley for a quick presentation on the expo hall floor. Get up to speed with the latest Plumbing technology and trends like SureSeal a proven trap seal device that blocks drain stink and bugs from entering the building through floor drains without using water.

Visit us at Booth #1704

28 Feb

How do I drain this water?

user Mr_Assault_08 asked:

Getting a new home and I noticed the water build up in the drain pan. It wasn’t here when they installed it, maybe after they tested the heater or something. But I’m worried the water here will eventually (years) damage the tank. So how do I drain it??

Answer: You could just sponge it out. At the big box hardware stores, they have sponges in the tile section that would work great.
– jjmcquade

Another alternative answer: Check your pressure relief valve. It’s probably blowing off. If it is, you’ll want to get a water pressure gauge and check your water pressure. If it’s above 85 psi you’ll want a water pressure regulator at your main and an expansion tank on the cold feed to the water heater. If you get this far make sure to brace the expansion tank so it doesn’t snap your water line and pump it up to match the pressure of your house. Hopefully it’s just a bad relief valve. Good luck bud
– Lostmyoldaccount88

source

09 Feb