Hello,

Could someone please help me with the problem with my 10 yrs old Trane AC unit.
Air handler model: Trane 4TTB3036A1000AA
Problem symptoms:
One day ago the air handler started making a sound like fan or motor starts, tries to speed up for 1-2 sec, then shuts off, then waits few seconds and tries again, and so on.

The fan on the compressor unit (outside) turns on and off at the same frequency.
I ordered a new capacitor and switched out the capacitor. The unit still cycles on and off every few seconds.

The unit was completely off for one full day while I was waiting for the capacitor to arrive. It is also currently off now since the new capacitor did not resolve the problem.

Are there any common easy to fix problems with such symptoms? Or should I just call an AC tech?

Thank you.

 

Is the contactor opening and closing in time with the cycling ?
Most likely yes and that means your system is low on charge and is cycling on low pressure.

 

Hi Pete,
Thanks for the quick reply. Yes - it does seem like the contactor (or switch) is opening and closing (physically) in time with the cycling.
I'll call an AC tech in the morning.

Should I assume there is a leak in the system or is this somewhat normal after about 10 years?

Thanks,
Kevin

 

You should assume it's a very small leak or a leak that has just opened recently. On a 10 year old system you'd want the service company to attempt to find a leak rather than just "charging and running".

 

Thank you for the suggestion. I did also just notice that (with the AC breaker off) the air handler is still cycling in a similar pattern while the thermostat was set to "fan". Would that still be a symptom of a low charge.

To me that seems like it would be unrelated - it seems like the fan on the air handler should run and just blow hot air??? and thoughts on this?
Thanks again.

 

The inside blower is doing the same thing ?
Is that a battery operated thermostat and have you checked the batteries ?
In cooling mode....is it displaying cooling ?

Possibly a stat problem. You can take it off the base and try shorting R to Y.
See if the compressor stays running then.
A short from R to G would keep the blower running.

 

ok - So now I have removed the Thermostat.

When I use a jumper from R to G the air handler seem to be running in very short cycles. I can tell this by listening to the filters in the return vents slightly lifting and then dropping about every 2-3 seconds.

I have flipped the circuit breaker for the AC unit back on and then use a jumper to connect R to Y. the result is that the outside unit/fan still also cycles on and off. about 4 seconds on and then 15 seconds off then it repeats.

I think if I were to go back and count the timing for the air handler - it would be timing out at the same interval.

 

Wow.... very interesting !

The first thing that comes to mind is that your air handler is somewhere that if it leaked could cause water damage. If that is correct.... then there may be a float switch on the drain system that is tripping.

Do you have a voltmeter ?
You need to check the voltage between R and C if the stat has a C terminal. It should be near 24vAC. When you touch R to G it should stay near the same voltage.

If you don't have a C on the stat..... check from R to Y. While watching that voltage connect R to G.

 

I'll get the voltmeter out and see what I can find out. Our air handler is hanging from the ceiling in our garage. not that you mention it - I did have a AC in an old house that did a similar thing when the drain line was obstructed and the full water pan made the ac go on and off. I'll also check and see if there is water filling up the water pan. Thank you for all the help so far!!!

 

I checked the drain pan under the air handler that is having the issue. It is completely dry. However, I do see that there is condensation on the exterior and it is cold to the touch. I wonder if the coils are frozen? could the on and off be a symptom of frozen coils? but how long should it take to melt? it has been off since yesterday afternoon (in Florida in a garage.....). Seem like it should have melted by now. Anyway, I think I'll try to check the voltmeter tomorrow. thanks again!

 

I'm usually only on at night but there are others that can help you.

That would have to be one solid block of ice. Here's the thing...... if you were low on refrigerant.... the inside coil would freeze up. I would expect it to have melted overnight especially in your heat. The outside condenser would cycle from low refrigerant but it should not affect the inside blower. That shouldn't be cycling.

 

Hi, can you access the control panel on the AH? Use the voltmeter and test between Common-G with the Tstat set to fan on, should be a constant 24 VAC, now call for cooling at Tstat and test between Common- Y should be constant 24 VAC.
sounds more electrical than refrigeration
Is there a wiring dia. You can post?
Geo

 

Thank you all again for the suggestions. I kept digging into the issue today and I found that my outdoor unit labeled #1 was working with my air handler labeled #2. So a mis-match on the labeling. What this caused was that when I was checking the drain pan on the air handler previously - I was checking the wrong one. So today, I ended up checking the other drain pan and found that it was full and the drain line was obstructed. I cleaned out the drain line and now the AC works normally again. I just wanted to close the loop on this. Thank you all.

 

Good job. Thanks for letting us know how you made out.