Surge Protectors- Either whole house or condenser unit only

[David Goodman]

What are your thoughts on the value of surge protectors for residential and light commercial HVAC condenser units?

The power supply appears to be poor in my area. I don't have a power quality analyzer. So, I don't have any proof of that. However, compressors on A/C units do seem to fail prematurely with great regularity here.

I have been looking at the Ditek DTK-120/240CM+ as a way to extend the life of equipment.

 

[kwired]

What are your thoughts on the value of surge protectors for residential and light commercial HVAC condenser units?

The power supply appears to be poor in my area. I don't have a power quality analyzer. So, I don't have any proof of that. However, compressors on A/C units do seem to fail prematurely with great regularity here.

I have been looking at the Ditek DTK-120/240CM+ as a way to extend the life of equipment.

I think you are barking up the wrong tree, AC motors are not all that sensitive to transient voltages, that are considered normal on the distribution system, and the motors themselves can be part of what produces some of the transient voltages. You may want to look harder at control issues and/or high/low voltage issues more so then transient voltages.

Main thing is anti- short cycling methods being built into the controls, otherwise if majority of them are on 240 volt single phase systems you must keep in mind those units are very likely rated for 208-240 so even some significant drop on a 240 single phase system still leaves them in their designed operation range.

If they are being taken out by lightning - you probably have more then just AC units failing.

ETA: don't forget to rule out poor installation practices also. A HVAC installer that takes shortcuts or doesn't know the proper methods can also create premature mechanical failures of the compressor.

 

[mgookin]

Is it a region of homes built around 15-20 years ago? Maybe it's just their time?

 

[David Goodman]

Is it a region of homes built around 15-20 years ago? Maybe it's just their time?

Yes, many are in the 15-20 year range. It is understandable that they will start failing.

A recent compressor that I worked on had been replaced twice in five years by another company. Unit is seven years old now. Another company (home warrantee company) had just come out and told the homeowner that her entire system needed to be replaced, but it wouldn't be under warrantee. So, big money. I looked at the condenser coil and found a obvious puncture from the outside that looked like it had been made with a scratch awl, but that is beside the point.

This was a 208-230V 1 phase unit. When checking the electrical at the unit's disconnect I had 243V between L1 and L2. L1 to ground was 121V. L2 to ground was 123V. However, with the disconnect pulled I had 97V from L1 to its lead to the condenser and 9V from L2 to its lead to the condenser. The condenser contactor was open at the time. Contactor was a single poll with a shunt (24V coil). I exercised the breaker at the main panel a few times. Replaced the contactor with a double pole, and I then had 7V between both L1 and its lead, and L2 and its lead with the contactor open.

After repairing the hole in the coil, the unit ran fine.

Can you help explain the potential readings of 97V/9V and 7V/7V from before and after exercising the breaker and replacing the contactor?

 

[David Goodman]

I think you are barking up the wrong tree, AC motors are not all that sensitive to transient voltages, that are considered normal on the distribution system, and the motors themselves can be part of what produces some of the transient voltages. You may want to look harder at control issues and/or high/low voltage issues more so then transient voltages.

Main thing is anti- short cycling methods being built into the controls, otherwise if majority of them are on 240 volt single phase systems you must keep in mind those units are very likely rated for 208-240 so even some significant drop on a 240 single phase system still leaves them in their designed operation range.

If they are being taken out by lightning - you probably have more then just AC units failing.

ETA: don't forget to rule out poor installation practices also. A HVAC installer that takes shortcuts or doesn't know the proper methods can also create premature mechanical failures of the compressor.

Thank you. All good points. I'm not interested in selling/promoting a product that doesn't truly benefit the customer.

 

[drcampbell]

I see you're in Nevada. Your short longevity might be due to the high temperatures. When the outdoor air temperature is 20°F-30°F higher, the compressor discharge temperature is going to be 40°F-60°F higher. The pressure will be correspondingly higher and more horsepower will be required to drive the compressor than in, say, Atlanta or Dallas. I don't know if "desert-rated" or "severe-duty" HVACR components exist, but they probably should.

You might reduce this problem by installing an oversized "smart" condensing unit with VFDs driving the compressor & fan. The brain box would operate the compressor at a reduced speed, just enough to match the cooling load, and the compressor temperature would be less. (using an oversized single-speed condensing unit would have little or no effect; it would operate for fewer hours each year but at the same temperatures & pressures)

Condensing units are insensitive to humidity and the temperature-humidity index; only the temperature affects how they operate.

... Can you help explain the potential readings of 97V/9V and 7V/7V from before and after exercising the breaker and replacing the contactor?

Not without being there. But I do notice that 24v + 97v = 121v; maybe one side of the 24-volt transformer secondary is grounded/bonded, (intentionally or not) forming a buck circuit, and you're looking at leakage voltage with an ultra-high-impedance voltmeter?

 

[MD84]

Can you help explain the potential readings of 97V/9V and 7V/7V from before and after exercising the breaker and replacing the contactor?

You said the contactor was open. When you checked with the single pole contactor the 9v was likely on the leg that was switched by the contactor. The 97v was likely on the leg that was not switched and was connected to the condenser.

Once you changed to a double pole contactor both lines were isolated from the condenser.

You were likely using a high impedance voltmeter. You were seeing capacitive coupling. The lower readings are because there was less wire and therefore less surface area. The single pole contactor allowed one of two legs to be connected to the condenser. This leg connected to the condenser has a lot more wire and a lot more surface area. Therefore the capacitance is greater and shows a greater voltage.

If you were to take those readings with a low impedance meter like a solenoid voltmeter you would probably not see a voltage.

 

[David Goodman]

You said the contactor was open. When you checked with the single pole contactor the 9v was likely on the leg that was switched by the contactor. The 97v was likely on the leg that was not switched and was connected to the condenser.

Once you changed to a double pole contactor both lines were isolated from the condenser.

You were likely using a high impedance voltmeter. You were seeing capacitive coupling. The lower readings are because there was less wire and therefore less surface area. The single pole contactor allowed one of two legs to be connected to the condenser. This leg connected to the condenser has a lot more wire and a lot more surface area. Therefore the capacitance is greater and shows a greater voltage.

If you were to take those readings with a low impedance meter like a solenoid voltmeter you would probably not see a voltage.

Excellent! That really helps with one of my primary concerns. I was using a Fluke T5-600.

 

[David Goodman]

I see you're in Nevada. Your short longevity might be due to the high temperatures. When the outdoor air temperature is 20°F-30°F higher, the compressor discharge temperature is going to be 40°F-60°F higher. The pressure will be correspondingly higher and more horsepower will be required to drive the compressor than in, say, Atlanta or Dallas. I don't know if "desert-rated" or "severe-duty" HVACR components exist, but they probably should.

You might reduce this problem by installing an oversized "smart" condensing unit with VFDs driving the compressor & fan. The brain box would operate the compressor at a reduced speed, just enough to match the cooling load, and the compressor temperature would be less. (using an oversized single-speed condensing unit would have little or no effect; it would operate for fewer hours each year but at the same temperatures & pressures)

Condensing units are insensitive to humidity and the temperature-humidity index; only the temperature affects how they operate.


Not without being there. But I do notice that 24v + 97v = 121v; maybe one side of the 24-volt transformer secondary is grounded/bonded, (intentionally or not) forming a buck circuit, and you're looking at leakage voltage with an ultra-high-impedance voltmeter?

Thank you. High temp. (70C) condenser fan motors are available, and those are the only ones we/I use here. Unfortunately I haven't found true high temperature compressors for residential applications.

VFD's and ECM's are definitely on the way. I haven't worked on any yet. So, I want to get my hands on a good reference book on VFD's, ECM's and their controls. The HVAC training sites I have been reviewing really don't have many materials on these. If you know of a good text for electricians, then please post it here.

 

[kwired]

Yes, many are in the 15-20 year range. It is understandable that they will start failing.

A recent compressor that I worked on had been replaced twice in five years by another company. Unit is seven years old now. Another company (home warrantee company) had just come out and told the homeowner that her entire system needed to be replaced, but it wouldn't be under warrantee. So, big money. I looked at the condenser coil and found a obvious puncture from the outside that looked like it had been made with a scratch awl, but that is beside the point.

This was a 208-230V 1 phase unit. When checking the electrical at the unit's disconnect I had 243V between L1 and L2. L1 to ground was 121V. L2 to ground was 123V. However, with the disconnect pulled I had 97V from L1 to its lead to the condenser and 9V from L2 to its lead to the condenser. The condenser contactor was open at the time. Contactor was a single poll with a shunt (24V coil). I exercised the breaker at the main panel a few times. Replaced the contactor with a double pole, and I then had 7V between both L1 and its lead, and L2 and its lead with the contactor open.

After repairing the hole in the coil, the unit ran fine.

Can you help explain the potential readings of 97V/9V and 7V/7V from before and after exercising the breaker and replacing the contactor?

If first compressor failure put contaminants in the system and they were not removed when the compressor was changed out it would shorten the life of the next compressor.

Your low voltage on disconnected circuit sounds like capacitive coupling as has been mentioned, measure with low impedance meter and I bet you get readings of zero.