hvac contactor

[Mgraw]

I think they are more reliable because of lesser number of parts.

I am sure there is some manufacturer out there that makes a good quality single pole contactor, I have not found them yet. There are also some 2 pole contactors that are junk also. But at least with two pole contactors I can find quality brands.

 

[iwire]

It would be looped ahead.

Draw it.

 

[iwire]

If you open this link http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/24abb3-1w.pdf

You can see on page one that for a single phase 208/230 supply they use a single pole contactor. On page two you can that for a three phase supply they are using a two pole contactor. In both cases the crankcase heater (CH) can only operate when the contactor is open. It is not run through the unswitched contactor pole.

It is not about increased reliability it is all about cost savings.

 

[T.M.Haja Sahib]

If you open this link http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/24abb3-1w.pdf

The page is not opening,man.

It is not run through the unswitched contactor pole.

It is run through NC contacts of the contactor?

It is not about increased reliability it is all about cost savings.

Would you at least concede reliability as a 'by-product'?

 

[augie47]

The page is not opening,man.

Opens fine for me. Interesting wiring configuration

It is run through NC contacts of the contactor?

No NC contacts... have never seen an HVAC with NC contacts

Would you at least concede reliability as a 'by-product'?

its usually about the $$$$$

 

[jumper]

And just how would that work unless there was a neutral involved?

Here is a link that talks about about it. It is some type of low amperage series resistor circuit that is internal to many compressors.

The run capacitance, off-cycle heat method, single-phase compressors are stopped by opening only one leg (L1). Thus, the other leg to the power supply (L2) of the run capacitor remains ?hot.? A trickle current through the start windings results, thereby warming the motor windings. Thus, the oil is warmed on the ?off-cycle.?

http://www.hvactroubleshootingguides.com/crankcase-heaters.html

In this schematic at the top right, there is a terminal harked H, I think that goes to the heater in the compressor through the start winding.

 

[kwired]

If you open this link http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/24abb3-1w.pdf

You can see on page one that for a single phase 208/230 supply they use a single pole contactor. On page two you can that for a three phase supply they are using a two pole contactor. In both cases the crankcase heater (CH) can only operate when the contactor is open. It is not run through the unswitched contactor pole.

It is not about increased reliability it is all about cost savings.

The crankcase heater is run parallel to the contact with a contactor that only switches one pole. This puts the heater in series with the compressor as well as the condensing fan. The compressor will have a lower impedance and bulk of current will flow through it. The resistance of the heater is pretty high so not enough current flows to cause any problem with the compressor or fan motor. If anything it helps warm the fan motor just enough to help prevent condensation problems in the fan motor.

Now consider this. Most guys replace these double pole single contact devices with a regular 2 pole when the original fails. by breaking both lines the heater will not have a complete circuit and you will effectively eliminate the heater from performing its function - not good for the life of the compressor.

Is it cheap? maybe. It is still a two pole contactor with different parts in one pole. A second set of contacts is probably more expensive but we are talking 20 or 30 amp devices here not 200 amp devices in your typical residential grade units total difference in cost is just a few dollars - if that.

 

[kwired]

Here is a link that talks about about it. It is some type of low amperage series resistor circuit that is internal to many compressors.



http://www.hvactroubleshootingguides.com/crankcase-heaters.html

In this schematic at the top right, there is a terminal harked H, I think that goes to the heater in the compressor through the start winding.

That "H" terminal is just the compressor side of the dual value capacitor. It is only active in the circuit when the contactor is closed.

This drawing does show the crankcase heater connected directly to L1 and L2 like all that I ever recall working on.
The only other thing slightly misleading is the indoor blower motor is shown connected to the leads to the crankcase heater. Don't let that mislead you into thinking it has anything to do with the heater, it is nothing more than an unswitched connection to L1 and L2.

 

[iwire]

The crankcase heater is run parallel to the contact with a contactor that only switches one pole. This puts the heater in series with the compressor as well as the condensing fan. The compressor will have a lower impedance and bulk of current will flow through it. The resistance of the heater is pretty high so not enough current flows to cause any problem with the compressor or fan motor. If anything it helps warm the fan motor just enough to help prevent condensation problems in the fan motor.

Why are you addressing this to me, I know that. It is why I said the heater operates when the contactor is open.:?

Is it cheap? maybe. It is still a two pole contactor with different parts in one pole. A second set of contacts is probably more expensive but we are talking 20 or 30 amp devices here not 200 amp devices in your typical residential grade units total difference in cost is just a few dollars - if that.

Yeah, Carrier only makes one or two units a year. :lol:

 

[kwired]

Manufacturers use single pole contactors because they are the cheapest contactors they can buy. In my opinion they are junk. If a HVAC guy tried to put one of those in my unit I would run him down the street.

Definite purpose contactors are not the same quality as NEMA contactors. Look at Iwires drawing and my comments on it. You would do a disservice to the owner to replace that one with a double break contactor.
The 1+ pole units are just as good or just as cheap as the straight 2 pole model from same manufacturer.

I think they are more reliable because of lesser number of parts.

Maybe only slightly It only takes one contact to fail and you are replacing the whole thing on the two contact versions. They are to cheap to waste time doing anything more but replace the whole thing.

I am sure there is some manufacturer out there that makes a good quality single pole contactor, I have not found them yet. There are also some 2 pole contactors that are junk also. But at least with two pole contactors I can find quality brands.

You get out of the definite purpose contactor lines to find those.

It would be looped ahead.

Looped ahead would be the drawing Jumper submitted. I thought that was the only way they were done. Iwires drawing shows a different way - I see some advantages to that method - like anti condensation heating within the fan motor.

 

[templdl]

I agree that the heater is important to consider when replacing with a one or two pole contactor. But, with A/C units where you may run them where the temperature if probably 75degF or above what is there a benifit of the heater?
Also, I can sure see the benifit of a 2p contactor as you then have 2 poles breaking the load and sharing the burdin instead on just one.

I agree that the heater is important consideration when replacing with a one or two pole contactor. But, with A/C units where you may run them where the temperature of probably 75degF or above is there a benefit of the heater?
Also, I can sure see the benefit of a 2p contactor as you then have 2 poles breaking the load and sharing the burden instead on just one which equals reliability.
If you did have a 2p contactor one could just jumper one of the poles bypassing one pole. And the advantage to that is when the pole being used fries then you simply reverse poles and jumper the burnt pole.
Those contactors can't cost but a buck to make but they aren't shy with their RP prices.

 

[Mgraw]

Definite purpose contactors are not the same quality as NEMA contactors. Look at Iwires drawing and my comments on it. You would do a disservice to the owner to replace that one with a double break contactor.
The 1+ pole units are just as good or just as cheap as the straight 2 pole model from same manufacturer.

Maybe only slightly It only takes one contact to fail and you are replacing the whole thing on the two contact versions. They are to cheap to waste time doing anything more but replace the whole thing.

You get out of the definite purpose contactor lines to find those.



Looped ahead would be the drawing Jumper submitted. I thought that was the only way they were done. Iwires drawing shows a different way - I see some advantages to that method - like anti condensation heating within the fan motor.

Generally most contactors that come on units are junk. There are some good quality definite purpose contactors that are availlabe but they are more expensive. I only use good contactors. You are doing your customer a disservice by using junk.

Capacitance type heaters would require one pole staying hot. Never come across one of those. Other types can be wired on the line side of the contactor.

 

[kwired]

I agree that the heater is important to consider when replacing with a one or two pole contactor. But, with A/C units where you may run them where the temperature if probably 75degF or above what is there a benifit of the heater?
Also, I can sure see the benifit of a 2p contactor as you then have 2 poles breaking the load and sharing the burdin instead on just one.

I agree that the heater is important consideration when replacing with a one or two pole contactor. But, with A/C units where you may run them where the temperature of probably 75degF or above is there a benefit of the heater?
Also, I can sure see the benefit of a 2p contactor as you then have 2 poles breaking the load and sharing the burden instead on just one which equals reliability.
If you did have a 2p contactor one could just jumper one of the poles bypassing one pole. And the advantage to that is when the pole being used fries then you simply reverse poles and jumper the burnt pole.
Those contactors can't cost but a buck to make but they aren't shy with their RP prices.

Generally most contactors that come on units are junk. There are some good quality definite purpose contactors that are availlabe but they are more expensive. I only use good contactors. You are doing your customer a disservice by using junk.

Capacitance type heaters would require one pole staying hot. Never come across one of those. Other types can be wired on the line side of the contactor.

I can get good quality definite purpose contactors from a HVAC supplier for less than 20 bucks. sometimes they have them on a special for only 13 dollars. This is true 2 pole units, Cutler Hammer, 25 amp contactors, with 24 volt coil.
You are not going to find much better quality in a compact definite purpose contactor - similar quality yes, better no. If you go with non compact definite purpose contactor you get better quality of device but it cost at least 2 or 3 times as much - pick what you want for a replacement if you have no faith in the compact models. They are usually just fine for up to 2.5 ton units maybe even 3 ton.



What is a capacitance type heater? The heater in the schematic that Iwire provided in a link is a resistance heater - it is just in series with the load switched by the contactor when the contactor is in a state of rest and bypassed when pulled in.


Most AC units do not have a crankcase heater - they are not needed when temperature is cold outside. If you have a unit that is needed when it is cold outside they can be ordered with a heater. Heat pumps usually have a heater as they are used in the cold. It does not take very much heat to keep the oil warm enough to prperly flow - that is all the heater is for and they usually have a thermostat to shut them down if temperature is high enough.

 

[Jraef]

Learned something today. My new unit may be so equipped. Someone else installed it. Does have a 2P disconnect though.

In addition, they will use a 2 pole contactor to switch a 3 phase motor. Same issue. They are saving $2 in the cost of the contactor not having to buy that 3rd pole. There is nothing in the NEC that prevents this, only that there must be an OL in all ungrounded current conductors and that anything designated as a disconnect must open all lines. The elevator industry does this too.

 

[templdl]

I can get good quality definite purpose contactors from a HVAC supplier for less than 20 bucks. sometimes they have them on a special for only 13 dollars. This is true 2 pole units, Cutler Hammer, 25 amp contactors, with 24 volt coil.
You are not going to find much better quality in a compact definite purpose contactor - similar quality yes, better no. If you go with non compact definite purpose contactor you get better quality of device but it cost at least 2 or 3 times as much - pick what you want for a replacement if you have no faith in the compact models. They are usually just fine for up to 2.5 ton units maybe even 3 ton.



What is a capacitance type heater? The heater in the schematic that Iwire provided in a link is a resistance heater - it is just in series with the load switched by the contactor when the contactor is in a state of rest and bypassed when pulled in.


Most AC units do not have a crankcase heater - they are not needed when temperature is cold outside. If you have a unit that is needed when it is cold outside they can be ordered with a heater. Heat pumps usually have a heater as they are used in the cold. It does not take very much heat to keep the oil warm enough to prperly flow - that is all the heater is for and they usually have a thermostat to shut them down if temperature is high enough.

I haven't looked at the schematic of my Carrier A/C unit but what you stated makes sence, that a heat pump would have heater because they are more likely be in a cold climate when an A/C would not. But, I am going to make it a point to see if I can dig up a copy of the scematic. I am one that replaced my contactor with a 2P and purchased a spare to assure that I have one at hand. I also don't expect to have a need for the the 2P replacement because now I have 2 poles now that are breaker and sharing the load.

 

[Jraef]

I think they are more reliable because of lesser number of parts.

Exactly the opposite is true. In a single phase 230V circuit here in North America, half of your complete circuit is always hot. If one pole welds shut but the other one still opens, the unit is still off. If you use only one pole and it welds, you lose the motor. But all they care about is that other $2 in component cost and that it outlasts the warranty.

By the way, having been on the inside at Siemens (who got OUT of the DP business last year because there is no money in it now), the average price to an OEM like Carrier and Trane for a 20A DP 2 pole contactor is around $9, a 1 pole is around $7. When they sell it to you for $25 they are laughing all the way to the bank.

In my mind, DP doesn't stand for Definite Purpose, it stands for "Don't Purchase". DP contactors are the lowest of the low in terms of QC and reliability. They are ALL the cheapest junk made that can technically still be called a contactor. 90% of them are now made in China by prisoner/slave labor, the rest are made in India but the Indian mfrs are losing out because their incredibly cheap labor force is still too expensive compared to forced labor in China. That's why Siemens got out, their production was in India and they couldn't compete unless they went to China, but the German Government is much more stringent about where mfrs contract for assembly labor and the Siemens team could not find a contract mfr in China that was not using forced labor of some sort, except from those that were on par with India, where Siemens already knew they couldn't compete.

The old story, you get what you pay for...

 

[kwired]

I haven't looked at the schematic of my Carrier A/C unit but what you stated makes sence, that a heat pump would have heater because they are more likely be in a cold climate when an A/C would not. But, I am going to make it a point to see if I can dig up a copy of the scematic. I am one that replaced my contactor with a 2P and purchased a spare to assure that I have one at hand. I also don't expect to have a need for the the 2P replacement because now I have 2 poles now that are breaker and sharing the load.

Schematic is probably inside of the cover of your unit. While cover is off just look to see if there is anything tied to supply side other than supply leads. If nothing else you have no heater - or if there is one it has had its supply moved when contactor was replaced and been made ineffective.

The 2 pole contactors fail just like the 1+ pole units. Maybe have a little longer average life but they do fail.

 

[kwired]

Exactly the opposite is true. In a single phase 230V circuit here in North America, half of your complete circuit is always hot. If one pole welds shut but the other one still opens, the unit is still off. If you use only one pole and it welds, you lose the motor. But all they care about is that other $2 in component cost and that it outlasts the warranty.

By the way, having been on the inside at Siemens (who got OUT of the DP business last year because there is no money in it now), the average price to an OEM like Carrier and Trane for a 20A DP 2 pole contactor is around $9, a 1 pole is around $7. When they sell it to you for $25 they are laughing all the way to the bank.

In my mind, DP doesn't stand for Definite Purpose, it stands for "Don't Purchase". DP contactors are the lowest of the low in terms of QC and reliability. They are ALL the cheapest junk made that can technically still be called a contactor. 90% of them are now made in China by prisoner/slave labor, the rest are made in India but the Indian mfrs are losing out because their incredibly cheap labor force is still too expensive compared to forced labor in China. That's why Siemens got out, their production was in India and they couldn't compete unless they went to China, but the German Government is much more stringent about where mfrs contract for assembly labor and the Siemens team could not find a contract mfr in China that was not using forced labor of some sort, except from those that were on par with India, where Siemens already knew they couldn't compete.

The old story, you get what you pay for...

I have seen many DP contactors weld a pole and it holds the armature to where the other poles remain closed. Seen this in both the compact units seen on typical residential AC units as well as 60 and 75 amp three pole units. Usually happens when the contactor closes on a short circuit or ground fault - so overcurrent device ends up tripping anyway. Protection of the motor is not too important anymore if the failure of the motor was the reason for fault current.

 

[T.M.Haja Sahib]

The contacts weld only when the magnitude and duration of current flowing through it is above its design value for fault current and this can be prevented by providing suitable upstream protective devices.So if it happens again,who is to blame?

If you use only one pole and it welds, you lose the motor.

 

[iwire]

The contacts weld only when the magnitude and duration of current flowing through it is above its design value for fault current and this can be prevented by providing suitable upstream protective devices.So if it happens again,who is to blame?

We provide the protection that we are required too, the contacts still fail when they close into a short.