Hello, Not wanting to change subjects but the area of HVAC did come up. Here in the south of Florida the AC is used almost the entire year. The relay in the outside compressor has had to be replaced about every 4 years. This seems a bit too much or?? I know it was the relay because I checked myself. This is the relay recommended by the manufacturer size-wise. One time the repaired man (when it was still in warranty) thought the power outages did not help. Any suggestions?? I was thinking of maybe a solid-state relay. About 2-3 times the cost but ?? Thanks roger.
I believe most A/C compressor units use what is called a contactor. It is true is is like a relay in that it is controlled by the coil connected to the thermostat, but it handles a LOT of current. There might be solid state relays that would work, but I think most of them are used in situations where the current being switched is less. Something you might consider if you look for a SS relay to take its place. You might also watch for the impact of the inductive motors on a SS relay. Some devices do not react well to the inductive spikes.
SSRs work pretty well for motors if they are rated for it. Since they are "zero crossing" devices they are fairly immune to spikes.One problem is most require a clean DC signal to turn them on and a lot of regular motor contactors will use AC coils so they are not direct replacements. I have had problems with the ripple on cheap wall warts causing half wave outputs from SSRs.
Get a size bigger contactor or one with bigger contacts. Some manufactures use pretty small contacts in my opinion. Install a whole house surge arrestor.
Solid state might need to be derated some for the heat. better check with the manufacture
They turn off at the zero crossing. There is a problem when you use them on 3 phase because there is really never a "zero" but I have had great luck with single phase loads. You can find SSRs up to 45a or so at the surplus houses like Hosfelt. I got some pretty cheap on Ebay a while ago too. I am using them all over the house for low voltage switching of lights and motors in my pool and spa. You can drive them directly from CMOS. The turn on looks like a LED behind a 1k resistor.
As has being mentioned by others in this thread, often the inductive spikes are the cause of contact failure. I solved a similar problem with my dishwasher by installing in parallel to the contacts a snubber network (resistor and capacitor in series, embedded into a resin block). Rudy
Impossible to say without knowing the electrical characteristics of the load (current, total impedance, etc.). Try to google for companies that sale snubber networks and send email to technical dep. with motor spec. They will tell you what you need. The resin block is used for mechanical protection, i. e. easy and safe to install on terminals. Rudy
HVAC equipment manufacturers are notorious for using the absolute cheapest devices they can get away with for electrical controls. The "relay" you describe is in fact a contactor as SQLit responded above, but for all intents and purposes it might as well be a relay. It is rated at absolute minimums for the load, referred to as "definate purpose". That term means that some engineer for the HVAC company was told to provide specs on a device that would do that specific function for at least as long as the original warranty period on the HVAC unit, but no more. If you get 4 years out of it you are probably very lucky as most HVAC equipment warranties are no more than 3 years.
If, as SQLit suggested, you replace it with an industrial rated motor contactor, you will most likely never need to replace it again. A typical DP contactor is rated for 100,000 electrical and mechanical operations. An industrial duty motor contactor is rated for 1 million electrical, 10 million mechanical.
My employer makes and sells Solid State Contactors but I would not recommend them for this application. They are a little too pricey for this considering what a good electo-mechanical contactor will cost. They are intended for applications where you may be experiencing 20+ operations per hour (as opposed to 10+/hr typical for elec.mech.)
The problem for you is not the concept, it is the execution by the OEM.
When our Lenox heat pump finally went south it was replaced with a Ruud. The Ruud unit used a ONE POLE contactor. (It had two sets of terminals but one set was just connected with a piece of metal. I guess "they" didn't want to confuse the installer too much.)
That said, the contactor was about as "beefy" as the one in the Lennox and that one outlasted the compressor.
Most HVAC manufacturers use only single pole contactors for their condensing units these days. The contactor is for control - not disconnect - purposes so it's an acceptable practice. BTW, the Ruud is about the cheapest POS unit you can buy. Chalk it up to customers insisting on the lowest bid/price for everything these days...
Maybe so. But I definitely trust my local HVAC man and that's what he picked. And the Ruud had a Copeland compressor (just like the Lennox it replaced). Frankly, it looks about as good as the Lennox unit. In any case, it has a 5 year guarantee. But I think it will last 10 years or more. If it fails out of warrentee, I will go for a high efficiency unit.
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