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Heat Pump Runs Hot & Cold

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Tool_maker
User Rank
Platinum
Re: Relay vs. Contactor
Tool_maker   5/14/2012 1:13:01 PM
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Today it is never safe to assume that an item needs replacement just because the srvice technician who makes the call does not know how to make the item work.

William K.
User Rank
Platinum
Heat pumps and quality of construction.
William K.   5/5/2012 9:28:04 PM
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Poorly crimped wires can certainly cause a whole lot of failures, mostly at the wrong times, like in winter, for heat pumps. The shuttle valves fail because they are of a quality not quite good enough for the job. In many circles that is called "value engineering."

One alternative choice would be to have manually operated valves to go from cooling to heating. Thgat would be much less convenient but it would be far more reliable. Of course, a large portion of our population would be unable to understand how to make the change over. 

Contactors, as opposed to relays, most often have contacts that are double makeand hence double break. This gives twice the open contact gap for no extra cost, and in addition, the contacts are usually heavier material to better handle the higher load current with les heating. Also, contactors do not use flexing wire in the current path.

Tim
User Rank
Platinum
Re: Heat pump
Tim   4/30/2012 8:58:03 PM
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My broken wire was straight from the control wiring to the control board.  It was just long enough to reach the board.  With the break, the technician added a pig-tail to make the wire long enough.

Larry M
User Rank
Platinum
Failed Crossover valve
Larry M   4/30/2012 3:42:45 PM
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I wonder if failure of the shuttle valve (usually stuck in the "cool" position during cold temperatures) is hard on the compressor, leading to premature failure. It seems to have happened to both of us. I've never heard anyone in the trades make that connection.

I also wonder if having that valve replaced was the best course. Since mine only seemed to stick when the temperature was below around 20F, I might have wrapped some thermostatically controlled heat-tape around it. I could have run a lot of years of 60 watts during cold temps for the $445 it cost to replace that valve and re-charge the system. This course was never suggested to me, and I thought of it after the repair had been done.

Larry M
User Rank
Platinum
Re: Heat pump
Larry M   4/30/2012 3:34:44 PM
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Yes, one of the reasons you have to repair these yourself is that the quality of service techs can be quite inconsistent.

I wonder if the "broken wire" in your unit was due to the same cause as mine: a wire connected between two surfaces in motion with respect to one another, causing repeated flexing. When it's really cold and the wire insulation becomes stiff, all the flexing is concentrated at one point. That point (in my case the base of the connector crimp) breaks.

Tim
User Rank
Platinum
Heat pump
Tim   4/26/2012 5:41:31 PM
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Our York heat pump had a similar issue where it would freeze up in a big block of ice in the winter and stop heating. Initially, the service tech just said it was low on charge and added Freon. It still froze up after he left. A different technician came out and checked the wiring to see that one of the wires controlling the main board was broken. After removing about 2 pounds of Freon, the tech restarted the unit and it defrosted just like it should.

richvan
User Rank
Iron
Re: Relay vs. Contactor
richvan   4/26/2012 2:14:18 PM
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I had recently replaced a 12 year ol Bryant heat pump for the same issue of the shutle valve being stuck.  I was told that since it was in the cooling position for such a long period of time that it was just frozen in place.  I had spent $300 for a repair person to switch out the valve and recharge the unit.  A month later it quit working and was told the compressor was gone.  Now $4300 later I have a new heat pump.  These things have gotten to the point where thay are throw aways.  They are not built like they used to be.  Comapnies are more concerned wiht getting a product to market and side stepping the critical part of life cycle testing.

oldguywithtoys
User Rank
Silver
Re: RELAY vs. CONTACTOR
oldguywithtoys   4/26/2012 12:00:10 PM
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I'm old enough to remember the old terminology and the short-lived confusion in going from condensers - small ones were rated in mickey-mikes (micro-microfarads) - to capacitors rated in picofarads, and over the new prefix "nano" that slipped in neatly between micro and pico to eliminate fractional microfarads (although I still tend to write 0.01uF instead of 10nF).  The differences there were attempts to clarify and the new, clearer terms were quickly adopted.  The two terms "relay" and "contactor" are a bit different.  They coexist simply because "contactor" is a common name for a specialized form of "relay," designed for high power and used to control inductive loads.  It rolls off the tongue a little more easily than "high-power-inductive-load-rated-relay."  In other words, all contactors are relays, but not all relays are contactors.

OLD_CURMUDGEON
User Rank
Platinum
RELAY vs. CONTACTOR
OLD_CURMUDGEON   4/26/2012 10:46:43 AM
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These two devices have different names because they ARE different in design, NOT in function (for the most part).  A contactor is usually designed with a set (or more) of STATIONARY Contacts to which the circuit wires are attached (usually marked L1 (& L2. L3), and on the other side, T1 (&T2, T3).  A beam with a similar set of contacts rides above the these stationary contacts.  This beam is usually connected w/ a spring relief design to a shaft that is controlled by the coil of the contactor.  When the coil is energized, the beam is pulled down, making CONTACT with the stationary contacts, completing the circuit.  The load becomes energized.

A classical relay, including "ice cube" relays is usually a (or more) stationary contact(s) with an arm that pivots about an axis.  When the coil of a relay is energized, a linkage (of many different designs) causes the arm to swing, much like a door on hinges. 

IF you study old electronic schematics & parts lists for radios, etc. from the early days of electronic devices, you will notice that they used the word "condensor" to describe the COULOMB device of modern day.  The descriptive word capacitor didn't come into widespread usage until many years later.  Since automobiles, and in fact, products using internal combustion engines w/ a KETTERING style ignition system predate modern electronics, it is easy to understand why garage mechanics called the snubbing capacitor, a condensor. 

GlennA
User Rank
Gold
Re: Relay vs. Contactor
GlennA   4/25/2012 1:05:28 PM
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L.M.G.T.F.Y:  A control relay is commonly called a relay;  a power relay is commonly called a contactor.  There is a difference between 'control' and 'power'.  'Power' implies high voltage and/or high current.  Put a relay in a circuit where a contactor belongs, and it will arc and be destroyed.  There really is a difference.  Control voltage and switching voltage (and switching current) are the criteria for selecting a relay or a contactor.  Try searching for an 'ice cube contactor'.   Referring to capacitors - a tantalum capacitor has a different application than an electrolytic capacitor.  The condensor that goes with the points of your ignition would be poorly suited to power factor correction.  A capacitor also has to match its application.

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