Coleman 7448

[MStrawder1]

The plate on the unit says it's a Suncutter 7448, but I haven't been able to find anything online with that model number. My problem is this. I received the unit from a friend who used it for years, but it had set for about a year without being run. I wired it up to my place, installed the thermostat, and turned it on. Ran great for about 20 minutes, but kept flipping the breaker. He said it was because I was only running a 40 amp breaker, so I went and got a 60 for it. Hooked the 60 up and it actually had a flame shoot out of the breaker.

Put the 40 back on and began troubleshooting as after that, the compressor and fan (not blower) would constantly try to come on and then trip the breaker. As best I could figure (I know some about electronics, but not really A/C units), the contactor was bad because it kept pushing power through. I replaced the contactor and hooked the wires back up (pretty sure they were right), but I'm still having the problem with the fan and compressor trying to cycle on. I unhook the main power feeds from both (have two power wires for each), but they still hum unless I completely disconnect them. I can get the blower and heat running fine, but as soon as I give the unit power, unless I totally disconnect the fan and compressor, they come on.

The only components besides the internal fuse box with the blower relay are two caps, the contactor, and a transformer. Please help me with this mystery. By the way, the thermostat is brand new and this all happens with it shut to Auto for the fan and Off for the a/c. However, if I turn the fan to "on", the blower comes on perfectly.[/b]

[Robert]

Hi,

That's an old unit and being aged and then sitting unused for a year, sounds like the compressor is pulling excessive amps.


Get a wrap around jaw clamp ammeter and see what the compressor amperage is at start up attempt.


Setting t-stat to ON is for running blower continously and AUTO cycles the blower with a call for heat or a/c.


Why was the contactor bad, not sure I understood what you were saying there ?



Take care and best wishes,
Robert

[MStrawder1]

The contactor became my first suspect because the thermostat was set to off and the compressor and fan were still trying to come on when I turned the breaker on the unit on. It was my understanding that the contactor was only supposed to output power to those components when the thermostat sent the signal to it. The place where I bought the new contactor at opened the top of it and the components inside were quite corroded, so he told me that more then likely it was sticking in the "on" position. However, after replacing the contactor, they are both still coming on when I flip the breaker on the unit. Is it possible the new contactor was bad too, or is it something else? I'm fairly knowledgeable when it comes to electronics and can usually trace the problem down, but I know almost nothing about a/c units.

As I said, there's the main fuse box inside the unit that also has the blower relay in it, 2 capacitors, a transformer, and the contactor. So I know I'm limited on what could be causing it. I tried hooking it all up w/o a thermostat attached to it and had the same issue, but someone else told me that should happen w/o a thermostat on the unit. I really wanna get this unit up and running as I know the compressor and fan were replaced not very long ago. So I'm hoping to get some use out of it.

[Robert]

Hi,

Going to eat supper, then will get back on here and what we can find.

Since compressor and condenser fan have been replaced, most likely just a circuit/power problem.


While I'm gone, go to unit and trace the two wires attached to side of contactor for the coil. Follow them both from there to t-stat (one) and transformer (other one).


See if they have a bare spot and have came in contact with each other or the metal frame of unit.

IF so, then you have a direct short to contactor, but it is not strong enough to start them, just make an attempt.

The short would bypass the t-stat.

Test each contactor coil wire to good ground. What does one from transformer read ?

What does one from t-stat read ?



Thanks,
Robert

[MStrawder1]

There's actually 3 wires coming from the side of the contactor. One side has a wire going to the transformer and one to the blower control relay. On the other side of the contactor is a wire that also runs to the transformer. I tested the transformer and got 120 from one side of it and 240 from the other side. At the T-stat itself is a 24v signal. I forgot to mention that the fan spins at a very low speed unless I turn the thermostat switch to heat or a/c, at which time it kicks into normal speed. So basically what I'm looking at is all the components, except for the blower motor getting power, even with the t-stat set to "off". I may have hooked up a wire to the new contactor incorrectly, but I was having the problem before I replaced the contactor. Is there a wiring diagram for the contactors to show what the L1 and T1 spots are. I'm fairly certain if I had to, I could follow the wiring diagram for the unit and re-run those wires, but I'm not 100% sure about where I'm hooking wires to on the contactor.

[Robert]

Hi Marster,

Ok, I have a pictorial parts breakdown for your unit, but no wiring diagram as of yet. Had to dig out and dust off my old service manual.


It shows a transformer, contactor, ONE run capacitor and a couple fuses/fuse holders in controls panel.

IF it has two capacitors and a blower relay, they have been added.


The transformer has Primary-Line side that should read 240VAC.

Then the Secondary-Load side should read 24VAC .

Be sure you're reading those correctly.


With the added components, the wiring may have been modified and without a wiring diagram, you would be better off to have a Tech come out and wire it up for you.

On the secondary-load side of transformer, you'll have a 24vac terminal and a Comm. terminal.

From the comm., a wire goes to one side of contactor coil and another wire would go from that same contactor coil side to either terminal 1 or 3 at blower relay.

From 24vac side of transformer, a wire goes to RH or RC or R whichever your wall t-stat has inside home.

Then, from t-stat Y, a wire comes back out to other side of contactor coil.

From t-stat G, a wire comes out to either 1 or 3 of blower relay, opposite whichever the other wire from contactor went to.



At contactor, L1 and L2 are the two incoming LINE power wires from wall disconnect or inside home service panel, etc. .


T1 and T2 are two of the 3 wires to compressor.



Thanks,
Robert