Two Stage AC Question

[Al Moran]

I worked on a 2 stage carrier package yesterday (single compressor, double pole contactor, 208v) that would open the contactor every time the 2d stage kicked on. I suspect something is wrong with the windings or internal overload of the compressor but if that were the case I don't understand why it would run fine in first stage and then die immediately when second stage is energized. It loses the low voltage at the contactor and if I push the contactor in when it happens it runs. also, there are low and high pressure cutouts in it, when I checked the pressure in 1st stage they were 210/68 at 80 degrees oat. The second stage cuts out so fast I could not get a pressure or amp reading. The fla is 19 and it draws 12a in 1st stage.

[Stormin Mormon]

Your diagnostic skills have ruled out a bad compressor, or bad contactor.

The resi systems I've worked on, there is a separate YH and YL for the stages. Sounds like you might have a fault in the YH wire, some where. Might want to see if YH is used on this system, and if it's atached to the same wire at both ends of the run. Like brown at the thermostat, and purple at the board....

Second thing comes to mind, to ohm out the wire and see if there is a break in the YH wire, along the way. As you're an experienced tech, I won't bore you with details how to do this. Nor will I write how to pull the thermostat off the base, and force the unit into YH to see if it's a bad thermostat, or a bad wire.

As a new tech, enough things get me wondering. I do wish you the best, and please let us know how things resolve. Maybe there is a set of panties wrapped around the contator (grin here).

[AKS]

I don't believe what I am reading what a mechanics Dido

[Noon-Air]

For some reason I seem to have Al Moron in the killfile.....

First thing is... Is it a straight A/C?? or is a heat pump?? If a heat pump.... what mode was it in?? Did you try jumping out the individual pressure cut-outs to see if you have a bad one??

[Bob_Loblaw]

"AKS" wrote

More like you don't UNDERSTAND what you are reading....

[gofish]

I for one would like to know how in the hell you get two stages from a single compressor, unless it is that Bristol twin/single. And since when is carrier putting them in package units?

Post a model number Al.

[Power's Mechanical]

Unloaders? :)

unless it is that Bristol twin/single.

[AKS]

Good Morning Jackass you fill better to day Dido

[AKS]

Actually Two stage compressors are made by Carlyle, Copland and perhaps some others but not the way is described by Al Copeland type 6RB1 three heads 6 cylinder one head high pressure two heads low pressure. typically in (10 one head) and 20 HP it come mounted on top of condenser with liquid subcooler attached. Carlyle similar configuration but with 30 HP. I did not come across their smaller size's if there is one. Machines are use at 40 to 50 below zero, R-502 and R-404a.

Now if we were to look at electrical system I would say that two stage start you would be looking at three phase STAR DELTA START where would two pole contactor come in use sorry don't know. it seems that something is missing here. Dido say that

[Bubba]

[Al Moran]

I don't have the model number off hand but it is a package system on a commercial property, has a single scroll in it, has y1 and y2 connections (though the stat is not wired for 2 stage), second stage comes on by a time delay circuit, schematic indicates it's a 2 stage also, has a damper that actuates for outside air when it comes on, has a belt driven blower in it.

[Al Moran]

He's right about the compressor and contactor.

[gofish]

hey Al....... I know exactly which model you're talking about, and yeah they're typically installed with a single stage t-stat.

y1=Economizer cooling y2= compressor

you need to get your hands on the operational manual for the economizer, then and only then will you begin to figure out whats happening. It is entirely possible y1 settings are keeping y2 locked out during specific time periods, based on built in temps in the economizer controls package.

Now if you happen to have one of those two wire Carrier economizer bypass plugs, unplug the econo, plug in your bypass plug, and now y1=compressor, and goodbye carrier econo-horseshit.

[Al Moran]

I did that very thing today and it worked like a charm.