Air Conditioning - How do I test the relay? Blower won't turn off.

I have been reading the forums on this, and today I did some background research. I was hoping that somebody could help me figure this problem out.

Problem: Blower (Air Handler) Fan stays on no matter what the setting of the thermostat, position of the fan switch, or position of the Heat/Cool Switch.

System:
Trane Air Handler (circa 1994 is my guess) Model TWH030B140A1
Thermostat : some older model (no digital) Trane Weathertron
Heat Pump: A matching Trane model.

Operation of system: I just bought the house in Dec of last year and the heat worked fine (blower never turned off, of course) all winter. I have not tested the A/C, but I think it works.

My recent investigation: I found the relay, but I don't know how to test it. The relay is a Honewell ST82U 1004. It also has a Trane number on it of : 21c144385p01. What is the procedure for telling if it is bad. After I cut the power off, the blower was a bit flakey about coming back on, and seemed to be refusing to . I had to cut the circut a few times and pull the main breaker, but it did come back to ITS NORMAL ALWAYS ON state (meaning it was broken, but returned to that state after I poked around its guts).

Am I proceeding in the right manner, or am I off track on this one?

Thanks,

After I cut the power off, the blower was a bit flakey about coming back on, and seemed to be refusing to . I had to cut the circut a few times and pull the main breaker, but it did come back to ITS NORMAL ALWAYS ON state (meaning it was broken, but returned to that state after I poked around its guts).


Could you be a little more specific about what you mean by "flakey"..and "seemed to"? Describe exactly what it did, sounds you heard, how long it took to come on, etc. You could try to replicate and place your fingertip on the relay and see what you might feel while this is going on (whatever that is).

Because this fan ran so much you may have a bearing problem also. And even if the capacitor is good, it may have a hard time getting revved up if there is bearing/shaft wear. (Does your blower have oilng ports at the bearings?)

Also, the capacitor may be bad and causing any delay in getting the fan to restart. But for starters, you may want to (***with the unit absolutely turned off and the blower not spinning!!!***) to reach in the blower squirrel cage and try to spin it by hand and see if it easily spins and stays spinning for many seconds. (Is yours direct drive or belt driven?. Belt driven won't want to stay spinning as long)

You don't happen to have a fan control switch inside your unit where you pull out or push in on anything do you? Have you looked real good to make sure? Although with a stat that can do all the functions you say, I don't believe that type of switch with that on/off feature should be in there. But I would check it out anyway, because you never know what may have been added on at a later date.

Could you be a little more specific about what you mean by "flakey"..and "seemed to"? Describe exactly what it did, sounds you heard, how long it took to come on, etc. You could try to replicate and place your fingertip on the relay and see what you might feel while this is going on (whatever that is).
.

Actually, what I think happened is that I may have been confused about whether or not I moved the breakers etc. and I attributed my confusion to the flakeyness of the air handler.

I just cut everything off and when I turned it back on it came up fine. I did spin the motor and all is well. I think I got you off track by my posting. The "Blower Always On" is the state that it is in. Sorry about that. I did check for a internal switch and I do not see one.

So I guess my issues is with the Air Handler Always staying on. This has been the way the system has been for 5 months.

Thanks. Does this help you understand what is going on?

Not sure what you mean about the blower motor. But with stat to off and blower running take and hit the side of the air handler hard with your hand. If blower dont stop pull G wire off at air handler. If blower dont stop then kill power and pull wires off fan relay and ohm it out.


ED;)

Not sure what you mean about the blower motor. But with stat to off and blower running take and hit the side of the air handler hard with your hand. If blower dont stop pull G wire off at air handler. If blower dont stop then kill power and pull wires off fan relay and ohm it out.


ED;)


Hi,

Thanks for picking this thread up. I was referring to the squirel cage when I said "blower motor."

Regarding your diagnostic procedure. I beat the side of the air handler and it did not stop the blower motor. Removing the G wired did not stop it either. I have the relay pulled, but I am not sure what the results mean or exactly how to test it (where to obtain the readings). Can you give me some idea? I have poked around it a bit.

WITH MY OHM METER SET on 2000

The long red (thread-like wound wire which looks like a big spool of thread) has two places where it is soldered to tabs. The resistance there is 11. The connectors which mount the relay to the circuit board are also 11.

The two tabs that come out of the circuit board (one had a grayishish-purple - not a gray wire with a purple tracer, but a grayish purple wire on it and the other had a green wire attached to it) was 675 ohms.

There are a bunch of other things I could test. I have tested contunity at all the other terminal combinations (ie. all the ones except those I mentioned above) and all are not continuous and I could not get any OHM readings on any of the combinations. Does this make sense? Sorry I don't really know all the proper terminology.

thanks a million for helping.

It sounds from your descipt that you have a fan relay switch as part of a solid state board... which I have a feeling, without knowing your unit, that this could be a fan timer set up, and you may end up needing a new board. If that relay is soldered to that board (is it???), I don't think you can get just the relay. I think you have to buy the whole board which may cost around $100 or more, if you can get a parts house to sell you one (without being an HVAC person). Does that board have a number of small square black boxes on it along with transisitor-diode looking thingies, with a lot of wires plugged into it on spade connectors?

Let's see if Ed can weigh in on this more.

It sounds from your descipt that you have a fan relay switch as part of a solid state board... which I have a feeling, without knowing your unit, that this could be a fan timer set up, and you may end up needing a new board. If that relay is soldered to that board (is it???), I don't think you can get just the relay. I think you have to buy the whole board which may cost around $100 or more, if you can get a parts house to sell you one (without being an HVAC person). Does that board have a number of small square black boxes on it along with transisitor-diode looking thingies, with a lot of wires plugged into it on spade connectors?

Let's see if Ed can weigh in on this more.

Hey DaVeBoy,

The relay is not soldered to the circuit board. It has a slot and tab mount. I just seperated the two. How do I tell if it is the board or the relay (or was my prior description enough)?. The board may or may not be fine. Everything looks fine, except for one solder joint on R2 (which I think is a resistor. It is mounted so that it is sticking above the board in a triangle like arrangement. that R2 part was too long to mount on the surface of the board). Anyway, I have zero small electronics experience (for the most part). The joint in question does looked slightly baked, but it is not blown out. (I know, my descriptions stink, huh).

My board is a honeywell 201282h


Any ideas how to tell if it is the board or the relay?

Thanks again!

Hi guys,

I called a local shop and found a replacement relay/board combo for 26.00. At this price, it didn't matter if the relay or the circuit board was causing the problem.

I installed it and now the blower operation is proper.

You all saved me a bunch of money and I appreciate your help.

For people who might be using this thread in the future, I will close it out with a few comments.

1) The replacement relay did not look anything like the original. It was what trane specified as a replacement. It did come with instructions and the tab connectors were labeled with the same nomenclature as the original. The price from my local vendor was nearly 30.00 (+shipping) LESS than I could find it online.

2) My replacement part was RLY02807 (which also replaces RLY 02257)

3) I would highly, HIGHLY, suggest putting masking tape and labeling the wires when you take them off. Unless you are a hvac person, this will make the job easy. If you don't do it, you could get into a mess.

4) Did I mention how important it is to do #3 above?

5) This should go without saying, but there is typically more than one place where you have to turn off power to the air handler!

Thanks!

$26...and you did it al by yourself? What a deal!!!!! Maybe they forgot to put the 1 in front of the 2. :)

And the last board I changed out had no less than 12 wires and I wrote down where they all went...believe you me. :)

$26...and you did it al by yourself? What a deal!!!!! Maybe they forgot to put the 1 in front of the 26)

yes, the price was right. Better yet, i am no longer wasting money and, equally importantly, not wasting energy with having the blower motor turning 24/7. It has gotta be easier on the components not to be turning either.

I figure a service call would have cost me 300 or more. That would be my guess anyway.

thanks again.

Hi there,

First of all: I'm new to this forum. I found it by google searching the pcb number that's printed on my time delay relay. I hope this thread is still alive.

I'm having exactly the same problem as cruiserparts.
Now as I am a technician it was easy to find out that the relay is functioning. When putting the 24V ac on it it opens and closes and the motor starts and stops.

The problem is on the timer PCB. After checking the fuse resistors and checking if the Transistor/FET (I can not determine from the info on it) is not short circuited I concluded that the mc14541 must have died. So I replaced it But No still the same problem.

So I started drawing a schematic of this PCB and reading the Datasheet of the mc14541. Either I'm making a mistake in the drawing or I'm Not as good as a technician as I think I am as I do not understand the design Honeywell/Trane did here. And it's such a simple peace of electronics.....

Does any body have the schematics of this small PCB? Or found what is the problem is?

I can also contact trane for a replacement here in greece which I will if I can't fix it. In this case it's not so much a matter of money as the knowledge that this must be simple to fix.

I would not mess with it. These boards are not meant for a mere human (technician or not) to troubleshoot. They are disposable IMO. It sounds like you have some good electronics knowledge you may want to save the old board for a rainy day to play with in your shop or something.That board is less than 60 dollars at most HVAC supply houses. No technician that is working by the hour could justify charging a customer to troubleshoot a board that costs less than a hour of his time on which he may spend 2 hours and still not repair it. Just economics you know. It does sound like a challenge though for a determined DIYer. Good Luck. You may want to try a electronics forum they might have some suggestion on how to test all those itty bitty little parts and pieces but I bet you would have to unsolder each one from the circuit to do a proper test. MEGA DISASTER LOL

thx for your response. You're right. Economicaly just looking at it is already more expensive then the pcb itself. But if by chance anyone has ever found what's wrong I could learn from it. As this chip works with 8 to 18 volt dc signals and Airco systems work with 24AC honeywell did a some simple trick with diodes but I don't get it..... '

The solution to the probem is one phone call to trane but I'm puzzeled by this design.