Trane Condenser Unit - Compressor starts and quits

[jeauxkewl]

Hi Gang,

 

I have a 17 year old Trane 3.5 ton unit (model TTP042C100A4) that has developed a problem. The outside unit starts but the compressor eventually quits. I had my trusted advisor over who looked at the unit and said the coils were filthy, probably just overheated. Cleaned the coils, said everything else looked good. Well, the problem returned almost immediately so I went ahead and replaced the run capacitor and changed the start capacitor/relay - these have a factory hard start kit - with a 5-2-1 kit. The unit started with no problems so I buttoned it up and went about my business. Well, it's 80 degrees in my home again so I'm thinking that the thermal limiter is shot and either that will need to be replaced or bypassed (if there is such a way) or else I'll be in need of a new compressor or more likely a new unit.

 

Before I invest much more time and money, is there anything you can suggest in terms of things to check?

 

Here are symptoms:

 

Condenser fan runs

Compressor starts and eventually stops

Sometimes I can get it to restart, other times it takes quite a long while.

New capacitors (except fan run capacitor) and start relay.

 

Fan continues to run so avoiding the contactor at this point.

 

Suggestions?

 

[BryanS]

How well were the coils cleaned? From the inside out with a coil cleaner? Some coils are a 2 piece and can have a layer in between them. I've seen pictures of a layer of stuff in between like milk weed etc. Sometimes if your charge is to low the compressor can overheat. My bro in laws parents unit is like 27 years old and that happened to theirs. Tripped out because it was leaking out the liquid line shutoff. Compressor took a crap though the next year because I didn't have time to fix it right.

And the thermal overload is built into the compressor windings, so their n won't be any replacing that without a whole new compressor.

[jeauxkewl]

No coil cleaner, just a water hose. I can pull the top off tomorrow and hit it from the inside to see if I can get some more gunk out of it. There shouldn't be any weeds in it, I have a concrete pad surrounded by bull rock and keep the weeds at bay for the most part. Will definitely give it another go.

 

Suppose I need a new unit -  I'm not really keen to spend a ton of money on replacing the entire works to R410A so I'd like to stick with R22. Any recommendations on that front? I see a goodman GSC130421 that seems somewhat reasonably priced. Any thoughts on the quality or longevity? Am I setting myself up for heartache by matching it with the Trane furnace/handler?

[BryanS]

Not real sure on recommendation. Everything is going down the crapper quality wise. Need a good installer and most anything should be ok. I don't think you can mismatch like that. You will have different efficiency ratings so it may work but the efficiency will be different. It's not always weeds that get in thw coils. Milkweed is like the whisker looking seeds. They can blow in. A condenser coil should always been cleaned from the inside then the outside. You could probably pickup some cleaner at Lowes. Preferably a nonacid type cleaner. Just clean it off well. Does the condenser fan motor look like it's running full speed? Typically, the units have a RLA (run load amperage) that can be checked to see if it's running harder or not.

I've never officially done HVAC service for a company. I've just been to two different schools and worked on a bunch for friends n family. I have zero install experience

[weswayne]

When the compressor comes on the indoor thermostat will call for cooling and that contactor will "make" and be drawn in.

Take note after the compressor starts to see what the contactor is doing when the compressor cuts off.

Is the contactor drawn in and the compressor shuts off (with power supplied to it) or has the contactor backed out or "unmade" (essentially cutting off the compressor)?

Wonder if there is a problem with the indoor thermostat?

[alamo1718]

First thing, ditto for a clean outdoor coil.  I use Dawn and Simple green. Spray it onto the coils and rinse from inside.

 

Amp draw on compressor will tell you how hard it's working. The RLA on the tag is running at full capacity, properly charged, 95 outdoor and 75 indoor.   It'll never run at that Amp draw but it gives you and idea of whether it is working like it should. Test on common. 

 

I'm assuming the condenser fan is running while the compressor is not. Next time the compressor shuts off, see if it's hot. It may be very hot. If it's very hot, cool with a hose for a couple hours or a bag of ice on the compressor shell to restart. 

 

Double check that you used the proper mfd capacitor. Also, did the new capacitor test properly out of the box? The wrong rating will cause the compressor to overheat.

 

Is the outdoor fan motor running as fast as it should? Check amp draw. 

 

Check for proper voltage. Low voltage will cause an overheat. 

 

If you have gauges and a way to test pipe temperature, check the pressures and temps. As a gross generalization, the low should be around 70 psi and the high should be around 225, 75 degrees inside and 95 outside. These pressures are dependent on indoor and outdoor temps. If the pressures are closer than that, i.e. 90 and 180, the valves in the compressor may be shot. 

 

Post pressures and line set temps if you can. Also post indoor and outdoor temp at time of test. 

 

Re replacement. The new 3.5 ton condensers do not match. If you install just a new condenser, you will lose efficiency. It will not pump the same amount of R22 the old one did, the indoor coil may starve for refrigerant. If you want to risk it, make sure to install the piston that came with the condenser in the old evaporator coil. Or install a 3.5 ton TXV on the indoor coil. It still may not work, then you're stuck. Also, the condition of the indoor unit may help the decision to go to 410A. If the indoor unit is 17 years old also, seriously think about full system replacement. 

Edited July 29, 2015 by alamo1718

[applianceman18007260692]

Check the amp draw on the compressor if it is way over what it should be it may run but it gonna get hot and quit= bad compressor.  Redneck method feel thecompressor after it quits, if it burns your hand it's probably stuck on start internal= bad compressor.

[jeauxkewl]

Voltage when running, both sides of contactor: 223VAC

 

Compressor amps, common: 11 amps

Fan amps: 1.1

 

When I started looking at it today, the fan didn't even start so I went ahead and replaced the fan capacitor. This unit originally had a dual capacitor but at some point they were separated based on what the tech had on the truck at the time.

 

Compressor run capacitor: 40mfd, 440V brand new

Start capacitor: part of the  5-2-1 kit, brand new.

Fan capacitor: 7.5mfd, 370 volt, brand new.

 

For what it's worth, I bought a cheap ammeter at harbor freight since my vintage amprobe grew legs in about 1984. Not sure how much faith to put in this one.

 

Interior temp: 79F

Exterior temp: 100F

 

I haven't yet drug the gauges out, not sure if they are any good any more, they are vintage 1983 Robinair. I was going to sit tight and see how long this cools before/if the compressor stops.

 

The coils don't look bad at all. I will make a run to the store for some cleaner in a bit.

 

[jeauxkewl]

Forgot to mention, compressor RLA is 17.0, LRA is 91 OD Mot is 1.9 FLA. Unless I'm missing something, all my readings indicate no electrical issues.

[applianceman18007260692]

11 amps sounds about right you cant go with LRA that dont mean shit.  You want to go with specified running amps. If the fan wasnt going that would certainly make her overheat and shutdown internal overload. maybe ya have it fixed now. Hope so.

[jeauxkewl]

Well, here's what I found - I let it run for a while and went outside to double check the running amps. When I went to clamp one of the fan leads, I moved another one and the fan quit. Moved it up and down and the fan was going on and off. Presumably an intermittent open in the wire, I went ahead and replaced the fan motor and all is well now. I suspect what was happening is the fan wasn't running at full speed or, depending on the wire expansion and contraction, it would shut off, causing the compressor to overheat.

 

Since I had the top off to change the fan, I cleaned the coils really good from the inside out Thanks very much for the help!

[alamo1718]

Nice catch. That would cause the symptoms you had.