TRANE Clicking Noise

[ftldelay]

I have a TRANE AC and heat pump unit (model TWV725A140A0) and when the heat is running, it will occasionally start making a loud clicking noise. Everything seems to be working fine, but the noise will wake us up at night and keep us awake unless we turn down the thermostat. I was finally able to open the front of the unit and remove the cover from the heater box while it was clicking and saw what was making the noise. I assume that I just need to replace this part, but frankly don't know what it is. I took a photo of the suspected faulty part, but this site won't let me post a link to it, so I had to break it down below. If someone could somehow tell me what it is and if it would make sense to replace it, I'd really appreciate it. Thanks!

The picture is - w w w .fataldelay.c o m SLASH Faulty_part.jpg

[Freon]

Since you have a heat pump I will assume you have electric auxiliary heat and that the photo you posted is in the indoor air handler. Nice work with the url.

That part appears to be the relay that switches the 240 volt power to the heating elements in the air handler when you need auxiliary heat. The clicking noise should be the solenoid being energized and causing the circuit to close energizing the heating elements. Why it is making a loud noise now is curious.

Does the noise last... I mean does the clicking happen for several seconds or is there just the one loud click.

It is possible the voltage to the solenoid coil is the problem if you hear repeated clicks (solenoid energized, click closed, solenoid de-energized, click open, etc.). Otherwise check for anything loose that may add to the noise. Use caution since there's 240 volts at that relay.

[ftldelay]

Thank you very much for your response. The clicking noise is a quick on/off noise with maybe a 1 second delay and then another on/off click. It could do it constantly for 30 seconds or go on for minutes at a time. It seems to happen more at night, but can happen during the day, although much less common.
I just borrowed a digital multimeter and hope to catch it in it's clicking cycle again and test both sides of the solenoid to see if the voltage is going on/off in the process. The blower of the unit is running constantly while the clicking is happening, so it does seem to be only this heating unit to be what's turning on/off.
I'm guessing that the round part above the solenoid in the picture with the 2 wires connected is a thermostat. Could it be possible that it is bad and sending a mixed message of sorts that would make this solenoid keep *
If I need to replace either of these parts, do you have any recommendation as to where I could most easily/cheaply get * My unit is a TRANE model TWV725A140A0 and the heating unit is model BAY96X1410A.
Once again, I greatly appreciate your help! Thanks!

[Freon]

The round part above the relay is most likely a high temperature limit safety there to insure the electric coils do not overheat. It is possible this is defective. You could TEMPORARILY jumper that safety and see if the clicking stops. It appears the high limit safety switch is in series with the power to the solenoid and if defective, could cause the solenoid to behave erratically.

[ftldelay]

Thanks again for your response. I replaced the thermostat relay as you mentioned and it's still clicking occasionally. I thought that might be what it was, so I had ordered one online prior to your response. A few years ago, when the clicking started, I replaced our main house thermostat control with a digital one, thinking that might be the problem, but the clicking continued. This year, it's been happening more frequently than in the past, so that's why I've been looking more into fixing it. The only other thing I could think to replace would be the solenoid unit. What would you recommend at this *

[Freon]

The clicking may be the solenoid but you still need to know why it's clicking. Is it really defective or is something interrupting the 24 volt AC supply to the *

When it's clicking I would measure the coil voltage (it's easy to access the leads to the coil part of the solenoid) and see if it's constant. If the voltage to the solenoid coil stays constant and you have clicking then the solenoid is bad.

But if the voltage fluctuates then the solenoid is doing what it should, following the voltage changes. We will need to trace the circuit to find what other safety switch is in series with the solenoid circuit, like the high temp limit we have talked about.

[ftldelay]

I was able to check the voltage of the 24V leads to the solenoid and it fluctuated when it clicked, so the solenoid appears to be fine. I tried to find any kind of other sensors or switches and didn't have much luck. I traced the 24V leads (as best as I could) back and they go into a box behind where the thermostat lines connect. I opened that up and noticed that they connect to a smaller solenoid (about half the size of the other one). There's also a transformer on top of that box that wires connect to.

After poking around, I turned the breaker back on and a few minutes later, the heat came on and it started clicking again. Rather than turn the heat down on the thermostat to shut it off and stop the noise, I tried turning the heat up hotter. When I did, the clicking indoors stopped. I came downstairs and heard the fan of the outdoor unit and it sounded like it was turning on and off slightly (almost like it was having a power dip). I went outside and heard a similar clicking from within that unit. I had opened that up earlier just to see what was in it and saw a solenoid, but nothing that I recognized as a temperature sensor. It did have a circuit board that everything connected to. I think one of the leads from the solenoid connected to the board and the other went to one of two large cylindrical capacitors. Another time, when it was clicking indoors, I listened to the outdoor unit and it was going on and off (and probably clicking as well) at the same time. It would seem like something is making it happen in both places.

I also noticed that the front of the box that the thermostat lines screw into has two lines connected to each of the color coded terminals. One line to our main thermostat, and another that runs to our outside unit. I'm not sure if that makes a difference, but thought I'd mention it. That box seems to be the common junction point where the indoor and outdoor solenoids connect, so maybe the small solenoid in there is at fault.

Is it possible that the new temperature sensor could also be bad * I don't know what the resistance should be, so I can't test it to be sure. I tried looking online, but no luck. Thanks again!

I was able to scan in a the air handler and heating unit schematics, which you can see -
The picture is - w w w .fataldelay.c o m SLASH Trane_Schematics.pdf

[Freon]

The solenoid you hear at the outdoor condenser may be either the main contactor relay that switches the 240 volts on and off to the unit ( you'll see very thick black and red wires) or it could be the changeover valve solenoid that switches the unit from AC to heating.

You are right about the junction function of the box inside. The Y and O wires from the thermostat pass through there going out to the condenser.

The fact that you have solenoids all clicking brings me back to the 24 volt system. The one common denominator is the 24 volt transformer you saw at the junction box.

The transformer will have a primary voltage of 120 volts AC and the secondary of 24 volts AC. You should see the secondary 2 wires attached to the control board. The primary (120 volts) will connect to the house power. I would measure the 24 volts where the transformer secondary connects to the control board. During a heating cycle that voltage should not fluctuate.

If it does fluctuate then we know why the solenoids are chattering. Then the question... is something in the circuit causing the voltage drop or is the transformer tired. Fortunately transformers are not expensive. The only other component could be the solenoids where the coil is shorted and when power is applied to the coil the short drops the 24 volts AC. It is easy to take the solenoids out of the circuit, one at a time, if need be.

[ftldelay]

The solenoid on the outdoor unit says 24V, but the wires look thicker than what I'd think would be necessary for 24V. One side has a red wire and the other is a blue and black wire. There are smaller wires connected to it as well (blue and red). I'm looking at a few pictures I took of it to try and figure things out. I wish I had taken a lot more pics. I'm guessing that it's really a 240V relay like you mentioned.

The junction box in the indoor unit has the terminals on the front with all the letters for the colors of wire connected to the thermostats. Like I said, there's thermostat wires going to the outdoor unit and also to our main house thermostat. When they meet at the junction box, all the wires are connected - not just the Y and O, like you mentioned. The terminals that are connected to both - W1, Y, T, G, R, O, and B.

You mentioned a control board that the transformer connects to. The only circuit board I can find is the one in the outdoor unit. I tried testing the voltage coming from the transformer as best as I could. All the 24V wires coming from it are crimped together with some other wires, so I traced those back to the back of the thermostat terminal panel. I measured the wires from the transformer and it fluctuated from 26.1V to 26.2V. I measured the Y and O wires and it was fluctuating from 25.6V to 25.7V. I was able to test it while it was clicking and got the same readings (that sure is fun at 3am). The transformer wires also connect to the small relay solenoid inside the junction box. I've yet to hear that relay click at all, and I'm not sure exactly what role it plays.

[Freon]

From the schematic there appears to be 2 relays. One is tied to the indoor blower motor. That may be the one in the box you mentioned. You should see a wire from the G terminal on the terminal strip going to this relay's solenoid. When you want the fan to circulate air, the G wire is powered at the thermostat causing the relay to connect the 240 volts to the fan motor. One more point... the transformer has a 240 volt primary, not 120, so be careful.

Now the above mentioned relay is a double pole relay meaning not only does it switch power to the fan motor but it also switch the ground side for the W terminal when there's a call for heat. The idea being, unless the fan is on, the heat strips can't be powered. The heat strips relay is the one you know about already. So you have 2 relays to check.

First, at the thermostat set the FAN to ON from Auto without calling for heat. That will energize only the fan relay. Any clicking at the air handler. If no clicking, leave the Fan set to ON as it is and now call for heat. Two things to verify... is there clicking at the air handler and is the outdoor condenser coming *

The B terminal at the air handler is the ground side of the 24 volt transformer. The R terminal is the 24 Volts AC. You should always have 24 volts (27 on your meter) between those 2 terminals.

I would check the wiring from the house to the unit. Make sure there is a very solid neutral and ground connection. Also check at the main breaker panel. Check all wire nut connections and any other connections at the relays. Do the same for the outside unit especially the control wires from where they leave the house to where they connect to the control board on the condenser. Being outdoors makes those wires and connections subject to more corrosion. Look closely at where the wires connect to the control valve solenoid.