Trane Defrost Issues

[Fredyiso]

Hi there!

I am the lucky owner of a Trane XR14 (2.5T) heat pump installed in June 2008. During the first winter, I called the installer because of weird defrosting behaviour: it was defrosting very often and for 10 minutes every time (it also had the timed defrost error code on the defrost board). So the installer came and said the defrosting control board was bad so he replaced it. I didn't pay too much attention to the unit afterwards but it seemed to defrost less frequently so I thought it was all good.

One year later... Since a couple of weeks, it looks like the trane is defrosting very often (sometimes 2 defrost cycles in less than 1 hour), eventhough there is no frost on the outside coil. When the unit defrosts, everything looks normal: I hear the reversing valve (tsishhh), the compressor starts with the fan off and the unit outside gets hot. The defrosting cycle lasts between 5 and 8 minutes.

So I called my installer and told him everything. In short, he's saying that he never heard of customer having unnecessary defrost cycles and don't really know what to do. To help him a little bit, I placed a temperature sensor on the freon line near my handler to see how often the HP is acting up. Here are the results for the last 12 hours. Dips around 10oC are defrost cycles. Spikes to 50oC are heat cycles. As you can see, it is almost defrosting after every heating cycle or so since this morning. The outside temp this morning is around 0oC. I went outside when I heard the reversing valve at around 11h20am this morning and there was no ice on the unit. Are these defrost cycles normal?? Any help would be really appreciated!

Thanks!

[Fredyiso]

BTW, I just tested the resistance for both sensors and they aren't too far from each other (27K for ambient vs 32K for coil). Something else caught my attention though: the defrost board I have installed is a CNT05004. Looking at the unit parts list though, the control defrost board should be a CNT02935 (which I think has been replaced by CNT04364). So here's my question for all the Trane's guru: Is it possible I don't have the right defrost board? My heat pump model is: 4TWR4030A1000A. Thanks again!

[SBKold]

As far as I know all the residential heat pump boards work basically the same (there are minor differences) and you shouldnt have that many defrost cycles. They use a nice demand defrost. I have had several bad outdoor expansion valves on Various ages Trane Heat Pumps this year. If there is a problem with the refrigerant circuit it will defrost more often due to lower pressures causing lower temp at the coil sensor. My recommendation is find a reputable guy who you trust and ask him to compare your refrigerant pressures to the Trane ServiceFacts Charts. These are axcessible by the service tech.

Have him test the thermistors thoroughly by heating them and them cooling them and watching them fluctuate

just a hunch but maybe you have a freon leak

[Fredyiso]

I have had several bad outdoor expansion valves on Various ages Trane Heat Pumps this year. If there is a problem with the refrigerant circuit it will defrost more often due to lower pressures causing lower temp at the coil sensor.

Thanks for your input! I will call him again tomorrow morning. For the outdoor expansion valve, you detect a bad one by looking at the pressures? Is it easy to differentiate a bad expension valve from a improper refrigerant charge?

[SBKold]

To be quite honest it can easily be overlooked. Your Trane unit should have all the pressure charts inside it so he can compare what the temp is outside and what the temp is inside the house and then it will give you a plot for what the pressures should be. As long as its in the ballpark of that chart than the valve and the freon level are ok.

[kytech77]

try moving the < No DIY instructions >

[Fredyiso]

try moving the defrost time to 60 minutes. I had one a couple of weeks ago that gave me fits. Also make sure the sensor is located correctly

I don't think there is a jumper on this board as it is an on-demand defrost.

[SBKold]

Youre right....On demand no jumper pin. I looks for what is called a delta T between the two thermisors. The unit has a preprogrammed map for a certain outdoor ambient, this temp means too cold must have ice or still warm enough to be no ice. That is why yours is reverted to the min time and deforosting all the time.

[kytech77]

ok...and you ohmed the sensors correct?

[Fredyiso]

The unit has a preprogrammed map for a certain outdoor ambient, this temp means too cold must have ice or still warm enough to be no ice. That is why yours is reverted to the min time and deforosting all the time.

So it might be the coil sensor getting too cold so the board thinks it has ice on it, thus limiting the air flow on the outdoor unit? Would that be the symptoms of an undercharged or overcharged unit in heating mode?

Best!

[kytech77]

make sure the sensor is in the correct place on the coil

[Fredyiso]

ok...and you ohmed the sensors correct?

Yup, I ohmed the sensors and they were a little bit off the chart, but not by much. My laser probe gave me -2 oC on the ambient probe.
The ambient sensor gave me 27Kohms, which is around 2.5 oC. The coil sensor gave me around 32Kohms or 0 oC. Should I be worried?

[kytech77]

is your outdoor coil dirty?

[Fredyiso]

Temperature graph for the last 24 hours. It looks like it went into defrost cycle 11 times in the last 24 hours (sometimes, the defrost cycle is splitted into 2 phases: could it caused by the aux strip kicking in almost at the same time as the inside temp reaching its target?)

[beenthere]

Just have your installer contact Trane, and have a Trane rep come out with him to diagnose it.

[Fredyiso]

is your outdoor coil dirty?
Outside coil is clean.

[kytech77]

its very possible to have another faulty defrost board. Have had any power surges? I would definitely get a quality technician to diangnose. You are correct, this is not normal

[SBKold]

Just have your installer contact Trane, and have a Trane rep come out with him to diagnose it.

Thats good advice. He will be able to quickly figure out whats going on without just changing boards and sensors.

[Fredyiso]

So the guy came last Friday. We discovered the defrost cycles were way too long. So he changed the coil sensor and still had the same issue. The thing weird, during the defrost, the base of the condenser unit wasn't receiving any heat. He mesured the pressures and got a low reading on the low side (50), while the high was good (300ish). So he added more R410. The defrost cycles were much quicker so we called it a day.

In the evening I noticed the compressor was not running anymore, just the outside fan. Basically, the compressor works for about 10 minutes and then it stops. The outside fan stays on so I basically think the safety is kicking in (the unit must be overcharged now).

I called back my installer and he wants to change my evaporator in the air handler now. Is it possible something is wrong with it causing a bad reading on the suction line?

[SBKold]

Were those pressures in heat ...with the outdoor fan running ....during the call for heat?

If it ran those pressures during a call for heat ...My money is on the outdoor TXV....like I recommended....Stop running the unit though! or you may have a shot compressor = $.

If it runs those pressure in cool mode (or during defrost cycle) than the indoor TXV could be the culprit. Which i would recommend changing the indoor coil to repair that TXV - - IMO.

[Stamas]

IMHO someone's just not being thorough enough in diagnosing. Find someone who is.

[SBKold]

----Agreed...... he left that thing to die a slow death!!!!

....FYI....not saying for sure you have a bad outdoor TXV....a good tech needs to diagnose that.....but I have one to put in today for the same complaint.....(granted those pressure were during heat mode). So its not that uncommon.

[Fredyiso]

Were those pressures in heat ...with the outdoor fan running ....during the call for heat?.

That is correct. Call for heat with outdoor fan running. The outdoor temp was about -2oC and inside return air was about 22oC.

Running on emergency heat for now... :(

[SBKold]

Id have to put my money on that OD TXV ...not likely indoor coil problem ...While running in heat and observing those pressures....upon switching back to cool are pressures somewhat normal? Thats another sign the OD TXV is bad. Going to replace mine in the field now. Same issue.

[jthom]

Looks similiar to a problem we had with a 4TWX5030 that was installed summer of 2008. The HP would constantly go in and out of defrost all winter during the coldest days. Bottom of outdoor coil would continually build with ice and never totally defrost. Yes- we also changed the defrost board and sensors.

Superheat and Subcooling as per manufactures specs, reclaimed refrigerant and weighed it right back in. Still - the bottom coil will grow ice.

Turns out we had a restriction in the bottom circuit and would not flow any refrigerant. We replaced the outdoor unit, brought the old unit back here to shop and have yet to cut open to disect. Should know what the rstriction was in a couple days but it could be anywhere in that lenght of tubing...

Actually swung by customers location this morning and they are happy with results.

[beenthere]

IMHO someone's just not being thorough enough in diagnosing. Find someone who is.


Adding a pound or 2 of refrigerant fixes all problems. :D

Like a steam heating system. Its not heating right. Increase steam pressure to 8 pounds, that'll get them heat. :eek:

[lentz]

:couch:Just raising to steam pressure to 6 pounds works for me.
(Just kidding)