3400A816 Electrical Issue

[Newdodge4me]

Hi Everyone,

I have found that Robert and the other admins here are excellent at providing guidance on some of these complicated issues. I am no novice at working on many different systems but these old units sometimes baffle me. I know I need to order a relay but need some help first.

This unit has been working flawlessly since Yall sold me the new sequencers back in 2008 except for last year the Fan Relay burnt out. I ordered a replacment and installed it, I had to put new spade terminals on one of the wires as it melted the insulation away. Well that worked great till last week when the tenant called saying there was a burning smell and the blower would not come on in AC mode. I purchased the schematics from the link on your page but it only gave me the schematics for the furnace unit, it didnt give me any schematics for the ac control box which is what I need to even attempt to verify the wiring and all.

Upon inspection I found that the Fan Control relay had burnt up (pic will be bleow) It burnt up the wire and end on pin 2, which if I am not mistaken is the load wire that feeds to the start cap and on to the blower motor. Well after replacing the relay and testing the unit for a short time (about 10 minutes) It seemed everything was ok.

After 2 days passed the tenant called again saying that the same thing had happened again.
I inspected the unit and found that the relay is totally fried this time a bit worse, it appears that something is overloading the relay causing excessive draw on this relay thus causing it to cook, and boy do I mean cook. This time it burnt mutiple wires going to the relay. I have cut out all of the burnt up wiring and started rewiring the damaged sections but I have a feeling that something is causing this to keep happening? I do know that when it happened the 1st time (last week) that there was a tremendous amount of heat comming from the unit when I pulled the service door off of the unit. I could not pinpoint the source I felt it may have been the blower motor as that is the only thing fed by the relay.
I didnt suspect the start capacitor as I didnt think the blower would even come on if the capacitor was open or shorted??

I would apperciate a second opinion on this issue. I only want to place one order for the needed parts so I can get this unit back up as quick as possibile.

Thanks again for all assistance for now and in the past.. It is always apperciated..

Sincerely
Roger

Pics Below

[Robert]

Hi Roger,

At the power source, does it have a breaker set up or fuses ?

The spade terminal with most damage in the pic, is it the incoming side of relay or the output side to motor ?


When this happened, was the a/c being used or the heat ?


To know for sure will take voltage readings, amp draws and close visual inspections of the breakers or fuses, relay, blower motor and run capacitor and all wires and connections.

Will need to ensure all are clean, tight and then that all voltages and amps are correct for at least a 30 minute continuous run time.


THEN, I would still place a fuse in the line slightly higher than normal amp draw to protect components in the event the circuit heated up again.


Also, if it were me, due to problems in past, I would rewire entire circuitry with new wire and quick connects.



Thanks,
Robert

[Newdodge4me]

Hello Robert,

This system has the FUSED supply instead of Breakers.
The side of the relay that burnt out was the Output Side (to he Blower Motor)
It was in AC mode when this happens(The system runs and cools initally, then it cooks shortly after)

I did replace all the Spade termainals when I replaced the realy the first time (last Wed) I tested and verified input voltages but didnt do any Amp draw tests just figured that the realy played out since (if my thinking is correct) it is only used when the Thermostat is calling for AC as the sequencer enguages the blower when a call for Heat is requested.

I didnt really think about it last night but after today I did remember something that may indiacte and help for further diagnostics.

keep in mind that I repalced this relay last wensday and it failed again less than 48 hrs later on friday as the temp finally got up and the need for the ac system was greater.(I doubt it even ran until friday mid day since I repalced the relay on Wed)

Anyhow what I am thinking is I did notice that on Wed when I went to service the unit the 1st time to where the previous picture showed, I did notice that when I pulled the panel off of the unit to access the hardware there was a tremendous amount of heat comming from the unit. I know it was not the heating elements as they would have burnt out fairly quickly without the blower on. I noticed that the Incomming side of the Blower relay and the Output side of the realy, well the wires were partially melted togeather. It just looked like the wire inslutation had just melted a little causing the wires to stick togeather but what if the conductor of both wires had acutally shorted togeather?? That would in essence supply the blower motor with one 110vac
and since the sequencer had not enguaged because the tstat was in the off position. Would the 110vac going into 1 side of the blower motor cause that extreame heat? Could that have burnt out the windings partially causing extreamly high reisitance in the motor thus causing the motor to draw a higher amperage draw from the relay than normal? Thus causing the relay to overheat and cause the relay to burn out and the wiring to melt? When I went up Sat morning after the tenant called and told me that it had did it again only after 2 days I was figuring that it was something simple but this time I pulled the access door from the control box and found a terribile mess, it was just a charred mangled mess of melted something It had burnt out the Supply side and the Output side this time and then shorted and burnt all the wiring in connected to the relay and Transformer.

I have already cut out all the damaged sections and decided to to just what you recommended Robert and to rewire the whole thing, that doesnt bother me to much. I need to find the schematics for the ac control box ( I purchased them last night from the link here but it only had the schematics for the electric furnace and nothing on the Ac side of things and how it ties into the sequencers and all. Since someone had already butchered the wiring I figured it best to make sure it is all correct.

I am thinking Mabe I need to replace the blower motor and the start capacitor?

What type of fuse should I use, since I have the thermoplastic wiring that is made for
hight temps not sure what type of fuse I should use? Buss with holder or just a standard Blade
fuse?

Sorry for this being so long, just like not to waist your time by not providing detailed information.

Thank You again Robert for all your assistance with this..
I know yall have the Paid assistance for diagnostics now and what email address can I use to send you a thank you for your time?

Sincerley
Roger

[Robert]

Hi Roger,

Fused disconnects are notorious for this, so check them closely. The prongs that hold the fuses become loose is most common.


The limits would turn the elements off and on, so can't rule that out.


In cooling mode, sequencer is out of circuit. Power would come to relay from fuse on one side of relay and from another fuse to blower for other leg of circuit.



Is the a-coil clean ? Filter clean ? Resistance on airflow can cause high amps.


My email is robert@mobilehomerepair.com .

IF the panel itself was hot to the touch, then be very suspect of the elements. Nothing else would cause that to be hot to the touch.


Thanks,
Robert