Current draw during startup - Carrier AC

[mikecales]

I have a Carrier Infinity Weathermaker 58MVP furnace and air conditioner. Newer AC with Puron technology that I believe is 3.5 ton unit. I live off-grid and last year ran the AC no problem with my 10KW military surplus diesel generator. I changed generators to a 12.5KW diesel model with an Isuzu diesel engine. I tried starting my AC and the blower motor came on and then when the compressor goes to start it just stops. It does not really seem to overly bog the generator. I am wondering if I have a problem with the AC compressor or if it is not getting enough power from the generator. I was outside and saw the fan on the outdoor unit start to spin and then boom it just quits. I would like to know what the current draw during motor start is?? I read in the manual that it is 30 or 32 amps (can't remember which) for locked rotor rating. Is that the max it draws during motor start-up or is it higher than the locked rotor rating?? Could it be that the power source is fine and there is something else at play here? Is there a way of using motor start capacitor to ease the starting?

[bbk]

Has anyone checked the voltage and amp draw out at the condenser? Since you changed generators?

[Shophound]

First of all, if you're generating your own power, I would think you'd have at least some idea of the quality of power you're receiving from the generator. Look at the nameplate on the outside of the condenser. It should state the minimum and maximum voltage ranges the unit can safely operate at. The generator should put out enough volts and watts to be able to satisfy this range.

Eliminating a supply voltage problem, if I saw a condenser fan begin to turn and then stop, my reaction would be based on:

a) did it slowly try to spin up and never come to full speed before cutting out? If so, may be fan motor and/or run cap.

b) does it spin, then lock up, spin then lock up? Bad bearings on fan motor.

If the condenser fan motor runs erratically, it will sooner or later cause the compressor to kick out on internal protector (overload).

Your best bet, of course, is to get a tech out there who's encountered this problem (except perhaps for homeowner generated electricity) a million times and can make the fix in his sleep.

Just curious...do you really save much money making your own power vs. what the grid would charge to give you power 24/7? Maybe you're out in the sticks and it's just cheaper to make your own juice than to pay for the power co. to run and hook up power to your house.

[mikecales]

Shophound,

Thanks for the replies. I am too far from lines to get them run to my house. I am in the process of putting in a solar electric system which will consist of 4200 watts of solar power. A 40,000 watt hour battery bank and inverters. The generator is a top of the line Isuzu diesel engine coupled with a Marathon generator head. This is not a gasoline powered portable type generator. It is a permanently mounted unit. Marathon and Isuzu are two well respected pieces of equipment. To try to describe the problem a little better. I called for cooling by turning the thermostat to cool position. I believe there is a short time delay programmed into the Carrier. The blower motor in the indoor unit came on and then when the compressor went to start it shut down within a matter of a split second. I have run the compressor off of both 240 single phase and 208 single phase and it ran fine off of both. It is now being attempted to be run off of 240 single phase. I am still really interested in the question of current draw during motor surge when starting and if that is given by the locked rotor rating?

Mike

[mikecales]

Shophound,

The old military generator unit had a watt meter on it and with AC running and normal household loads such as TV, washing machine etc the most it ever drew was in the 3500 watt range. Of course higher during the motor starting surge of the compressor. The new generator is rated at 12,500 watts. If the compressor were to draw 30 amps at 240 volts (I use this number assuming that the locked rotor rating is the maximum current the motor will draw and please correct me if this is wrong) that would be 7,200 watts.

Mike

[Irascible]

The 30 or 32 amp figure is probably maximum fuse size and/or minimum circuit ampacity. I just looked at the data plate for a 3 ton 10 SEER Trane air conditioner. Its locked rotor amps was 87. Yours will be in that ballpark. The LRA should be printed on the AC's data plate.

[bbk]

Has anyone checked the voltage and amp draw out at the condenser?

Or are you feeding it 110 volts thru a bad breaker?

[mikecales]

Irascible,

I got the locked rotor amps from the Carrier manual and will go back and check. Should there be a data plate on the outside unit? Does the unit actually pull its locked rating during start-up?

Mike

[mikecales]

bbk,

Good question and no I haven't checked for a bad breaker or called out my service tech yet. With our heat wave starting this weekend he is probable up to his ears in service calls right now. You are thinking that perhaps only one side of the breaker is feeding power to the compressor? It is a double breaker in the breaker box to get the 240 of course. In addition we have the fuses out near the outsoor unit. Is it possible we have burned out one fuse and it is only getting 110 volts because of that? The 30 amp breaker in the house is not tripping when the unit tries to start.

Mike

[Irascible]

Originally posted by mikecales
Does the unit actually pull its locked rating during start-up?Pretty much. But it's literally (usually) a fraction of a second.

You should find out if your compressor has a hard start kit on it. It could be OEM or an aftermarket product like KickStart. Either one can potentially reduce the duration of the spike in amp draw. I've had customers who had dimming lights and buzzing circuit breakers when their compressors started. The KickStart alleviated those symptoms. Make sure it's sized right.

[bbk]

Is it possible we have burned out one fuse and it is only getting 110 volts because of that?
================================================== ===========

WAAAAY!

[Irascible]

Where would the 110 volts be going once it left the unit? The only answer to that quesion that I'm aware of is a really bad one.

[mikecales]

Irascible,

Thank you kindly for the reply. Would my installer know if it had a kick start type of unit on it? I don't think at the point of purchase and installation that anything was added extra so if it is there it would have to be a factory type of unit. Who installs the kick start type of unit the HVAC contractor or an electrical contractor?

Mike

[mikecales]

bbk,

Does your reply of waaaayy mean that yes we could have burned out 1 fuse? When that happens the unit will try to start but can't? Excuse my ignorance if the answer should be obvious. I am trying alleviate my ignorance. I am an engineer but it is chemical and not electrical.

Mike

[Irascible]

The installer will know. A tech can let you know as well. You'd have an HVAC contractor install it if it didn't come with one. I carry a few on the van myself. It takes just a few minutes to put in. Even if it doesn't help this problem I'd probably leave it in (barring any goofball interactions that I'm not aware of between a generator and a KickStart).

The only way I know that a 220 AC could run or try to run on 110 with a blown fuse is if you have a short to ground in the unit. I have seen that before. I watched fan spin at a reduced rate while the compressor did nothing. But that was on an ancient system. We'd hope your brand new one didn't do the same.

[Edited by Irascible on 06-06-2005 at 08:23 AM]

[mikecales]

Irascible,

Thanks again. I have not had any problems up to now running the unit off of the old generator. I am highly interested in the kick start type of unit and have read of people installing motor start capacitors referred to as soft start capacitors to ease motor start draw for motors run on generators.

Mike

[pecmsg]

Mike
Are the breakers off when you start the generator?

[mikecales]

pecmsg,

I would say that the breakers are on when I started the generator. The generator had been running for a significant period of time before I turned on the AC and found I had this problem. The AC was in mode = off. I then switched the AC to mode = cool. It has a two minute (I think this is choosable). The blower motor then came on in the indoor portion (what I refer to as the furnace blower) and then it tried to start up the compressor and just wouldn't start. A spin or two on the outdoor fan unit and then nothing.

Mike

[pecmsg]

First get in the habit of starting the generator with all the breakers off. Circuit boards don’t like low and high voltage. ( TV / Microwave / Radios / Phone Etc.)
Second get a voltmeter and learn how to use it.

It sounds like you blew a fuse outside, but can’t trouble shook on a computer. Call your contractor to have the unit checked. Ask that he have a hard start kit on the truck. Good Luck

[tecman]

One question, when you say the compressor does not start, what happens ? Do you blow a breaker or does the compressor sit there and hum ?

What may be happening is that the new generator may not have as much "reserve" as I will call it to start the compressor. The ability of a generator to handle a start surge like that depends on the available torque (mostly inertia at that point) and the peak capacity of the generator. This capacity is a function of the amount of iron (laminations) and the winding wire size. Most newer generators are made right to spec, no extra so to keep cost in line with company profits. If the iron (laminations that carry the magnetic field) is at the limit, the magnetic field in the laminations saturates, and no more power above saturation can be drawn. If the copper (windings) are at the limit, the wire resistance will limit the available output current. I suspect both factors are in play. You should see a momentary voltage dip as the compressor tries to start, and as you said the engine does not lug. This would indicate a generator limit. The older mil unit was most likely built with more generator reserve, either because it was older and things were designed more conservatively, or it may have had as part of the spec the need to handle greater surge loads.

A hard start kit may help. Also the wiring to the compressor may be contributing a bit as well, since under these conditions any additional voltage drop might be just enough to tip the scale. If possible try to get some min voltage readings at the generator and at the compressor unit. Most Fluke digital voltmeters can measure min/max voltages and will capture the dip in voltage. If there is a significant difference between the generator and compressor, up the wire size.

paul

[mikecales]

Tecman,

Thank you for the reply.

What happens is it seems like it tries to start and then quits and this is very quickly. I was outside last night watching the outdoor unit when it tried to start. I would say the fan turned a couple of revolutions and then nothing. No humming. The digital thermostat blinks cool when you first turn it to the cool mode from the off mode. I think it has a 90 second or 120 second delay mechanism. Then the blower fan turns on and then the compressor starts. At this point the thermostat quits blinking cool and just reads cool. Whne I turned the thermostat to mode=cool it started blinking cool just like it should. Then the lower kicked in after a delay and then the compressor tried to start and the fan outside did the couple of revolutions and then it just quit. I went back in and the blower kicked off and the light went back to blinking and it was ready to go through its delay and try again. The 30 amp 240 volt circuit breaker in the house did not trip. Some folks here have indicated that one of the fuses at the outdoor fuse holder may have blown and to check it.

Mike

[mikecales]

Tecman.

How much difference does the hard start kit typically make on these motors? Is it a cheap enough type of add-on that it is worth trying just as a matter or course. I know we don't discuss specific prices here but I am trying to see if the order of magnitude suggests just automatically adding one for ease of operation.

Mike

[tecman]

Mike:

The hard start will not lower the initial in-rush. What it does is it gets the compressor running faster, wilch will shorten the duration of the inrush to a shorter time. This may help.

What is interesting in your latest comments is that it seems that something is shutting down the unit right away. It could be a controller in the compressor unit (if there is one), or it could be in your electronic thermostat (which you seem to have). What I think is happening is that one of these controllers is resetting, which will set a startup timer of 5 or 10 minutes (short cycle timer). This could be easily due to a voltage dip when the compressor tries to start, causing the controller to detect a power loss and restart the short cycle timer. If the thermostat is the culprit, it is most likely getting its power from a 24 volt control transformer in the air handler. If this is the case, it could be a voltage drop at the air handler, due to low incoming line combined with additional voltage drop at the air handler as the blower motor tries to start.

You could try a non-electronic thermostat as a test to see if it is the electronic thermostat. Solutions to this problem may be as simple as increasing the wire size to the compressor unit or air handler or both. Again trying to get voltage dip readings will point you in the right direction.

paul

[stevehvac]

Also don't forget that you will have a different control voltage going from 208 to 240. You must change the tranformer wiring. You may not have enough voltage to pull the contactors in.

[mikecales]

stevehvac,

The unit was originally set up to run on 240, then I switched my set-up to 208 and it ran fine. Then switiched back to 240 and it ran fine. So, nothing was changed. I was told by electrical contractor that most modern motors designed for 240 single phase ran fine at 208 single phase.

Mike

[stevehvac]

If it ran fine then it is a non issue but the eletrical guy is wrong on it makes no differance. It might not matter to the motors but the transformer could give you problems. If it is running on 240 volts and is setup that way then the transformer has the copper going around hundreds of times until it's reduced to 24 volts of control voltage. Now what happens when you have only 208 volts going into the tranformer? Ive found that you may get 22 volts going out. Then after running the t-stat and fan you have 20 volts. Then when trying to run the compressor you have 18 volt which isn't enough to pull the contactor in all the way.Once again it may be a non issue but switching the voltage can have an effect on the control power you have.

[cem-bsee]

and, you may have a pp sine wave from the new generator! = clipped waves

what is the rms voltage? the rms amperage draw? how good is your meter? how many times have you used this meter to read starting currents?

[mikecales]

cem-bsee

I think the meter you are referring to was the meter on the military generator I used to have. I never used it to look at the starting current.

Stevehvac,

I am running the system off of 240 volts now so there shouldn't be a problem with the transformer and 22 volts versus 24 volts. The data plate on the compressor lists the motor as 208/230 volts with acceptable range from 187 volts to 256 volts.

[mikecales]

I checked the fuses at the outdoor unit and both were good. That is they showed a short on the ohm meter. The HVAC techs here where I work believe the problem is in the 24 volt contact side of things. They believe the contacts are making and then breaking and could be a weak coil or thermostat issue. I have a call into the dealer who installed the unit and am anxiously awaiting to get him out to look.

Thanks to all

Mike

[jacob perkins]

Originally posted by mikecales
Stevehvac,

I am running the system off of 240 volts now so there shouldn't be a problem with the transformer and 22 volts versus 24 volts. The data plate on the compressor lists the motor as 208/230 volts with acceptable range from 187 volts to 256 volts.


Okay...what he was saying was this:Your transformer likely consists of different "taps" on the primary side,one for 208,one for 240.They should match the voltage you are presently feeding in...

You can check to see if the contactor is pulling closed or not,that should tell you something.

[cem-bsee]

no, I am refering to any troubleshooting meter for use on an electrical system -- should be one which reads the RMS values for alternating circuits -- usually costs more --

what is the control voltage value when the unit is trying to start? the "24v"

[mikecales]

Jacob,

The transformer was set up for 240 originally and that is what I am applying. When I ran the unit off of 208 I did not make any changes ( only out of ignorance that I was supposed to). Then when I switched back to 240 everything was still operating fine. That was last summer. After the winter I switched generators from the old one to a new one and am now having the problem. I wish I still had the old one so I could eliminate one of the two possible causes = generator or air conditioner?

Mike

[jacob perkins]

Originally posted by jacob perkins

Originally posted by mikecales

You can check to see if the contactor is pulling closed or not,that should tell you something.


Okay,it still sounds to me like the problem is in the control circuit.Of couse,I am only guessing based on what I read here.