Coleman 7335(?) Series Compressor Suddenly Stopped

[sgossman]

I started using this AC unit after about 2 years of no use. It started up great with no problems and was kicking out cold air great for about 3 days until the compressor just stopped in the middle of cooling.

I thought at first it was because it reached the target temperature but it was too warm in the room for that. No matter what settings or how low I set it I can't get the compressor to start again.

The fan works fine and I already checked all the capacitors and they are working (holding charges) as well. The fuse in the thermostat appears intact and the unit is not tripping any breakers.

I'm kind of stumped as to what else it could be. Only real suspect I have left is the start relay and apparently the exact type isn't around and I need to use some sort of replacement model I'm not sure of. Perhaps it could be one of the boards but I'm not entirely sure how to test those or what levels I would want. The only maintenance manual I've seen seems to require a specialized device to test various aspects of the unit.

I believe its part of the 7335 series but the model number has since worn away. Another number is 6799A381.

[sgossman]

Alright well as a catch up:
Replaced all capacitors
Replaced thermostat
I checked the windings again and they are still 5-4-1.

Replaced start relay, however I can't seem to get a straight answer on exactly what wires go where since the universal replacement has a different number of leads than the original. As such I am not sure where to plug in what color wires to what leads and I can't find any sort of replacement or wiring guide other than diagrams I already provided which I often can't decipher.
However when I wire my "best guess" there is no change in behavior. Red to T2, Yellow to T1, black and purple to T5.



Current state is I turn the thermostat on "Cool" "high Fan" it attempts to run but seems to struggle and will either quit on its own or trip the breaker.

[sgossman]

I did some more testing and I learned this "rapid clicking" is the work of the thermostat. I assume some sort of cut off due to not getting the responses it wants.

I learned this by (finally) learning I can bypass the thermostat outright by jumping Y (compressor) Green (high fan) and Red (12v).
When I do this I do not get clicking and the unit stays on but I do not get cold air. I only just started messing with it in this configuration but I noticed it did sound like the compressor would periodically try running (hums) and then gives up when I bypass the thermostat.

A cursory search leads me to believe this is the capacitors but I replaced the "Start" and "Run" capacitors with new ones that can hold quite a bit more. I didn't swap the "Fan" capacitor but the fan works fine.
EDIT: Swapped fan capacitor as well, seemingly no change.

[sgossman]

This might be "necroing" but its the same AC and relevant information.

I finally got around to replacing the thermostat since I found a maintenance manual and flowchart: http://www.cleggind.com/postal_tech/pdfs/AC2/airxcel_1976376%5B1%5D.pdf

Which led me to replace it. Good news is it has made significant progress, bad news is I have new problems.

When I switch the thermostat to "Cool" the control board and thermostat click incessantly in unison. The clicking varies in speed and sometimes will even stop for about 5 seconds and "run" correctly before more clicking. It sounds as if it is coming from a relay on the board. I suspect the one marked "K3."

The possibly good news is that its clearly putting out cool air, I just cant get it to stop clicking and run uninterrupted.

I'd be curious if there is some diagnostic way to bypass parts of the system, just get power to the unit outright for diagnostic purposes and bypass things like the thermostat.

[sayoung]

Take a minute and find what happened to your 120 across Run & Common . pins 1 & 3 of your harness , where/what do they connect to ?. The potential relay/start cap only helps start ( boost) the compresser & is only in the circuit for about 7 seconds max or you will need a new start cap. It's not even needed with a capillary tube or piston type metering device but is needed with most TXV 's. If compresser simply quit while running it is going to be an open circuit or the compresser has had a mechanical failure. Normally a bad run cap just won't let it start again once it shuts off. Could be as simple as a bad thermostat not calling for cool .

[sgossman]

sayoung wrote:
"Y" is the LOW voltage lead that controls the relay ( contacter ) that energizes compressor. The relay you posted early on is a start/potential relay for a Start capacitor. Sounds like what you ordered was a CONTACTER , totally different function .

This is what I ordered
https://www.ebay.com/itm/123744887539

Whose model number points to many listings all calling it a "Start Relay" and the diagrams and manuals for my AC also call the part I replaced a "Start Relay"

Diagram on the inside of my AC unit:


Diagram that came with the new start relay I ordered:

[sayoung]

"Y" is the LOW voltage lead that controls the relay ( contacter ) that energizes compressor. The relay you posted early on is a start/potential relay for a Start capacitor. Sounds like what you ordered was a CONTACTER , totally different function .

[sgossman]

Well its not "Open windings/Open internal overload" or "Shorted windings."

I was going to test for "Contactor not pulling in/ Contactor Failure" but I have no idea what "Y" is in this context since there is no "Y" label to be found. The top of the compressor says "S" "C" and "R" The closest thing to a "Y" any where I can tell is a yellow wire going between the relay and capacitors.

Here is the top of the compressor for reference.



In any case I don't think its the compressor, I think power isn't getting to the compressor for some reason despite the fan still functioning.

I got a replacement relay but its a 'universal replacement' with extra spots so I'm not sure if I have it connected right. The only info I had to go on is on the old relay spots marked "1" "2" and "5" so I connected the wires to the parts on the new relay marked "T1" "T2" and "T5."

There are also a "T4" and "T6" on the new relay which are "Common Park Terminals" per the included diagram.

[C_Schomer]

If that's with the compressor leads unplugged, that's good. Run winding ohms + start winding ohms = total ohms. So, R -W is the ends of the S and R windings, with the highest Ohms, so that means Bk is the common terminal.... between start and run windings. Bk-R is start winding cuz it's higher Ohms than run. Bk-W is the run winding... Bk is 120v and W is neutral during operation. Make sure all terminals to gnd., ohm infinite. This only means the windings ohm good and the internal OL is closed... could still have a locked or sticky rotor.
Unless things changed (got cheaper) there's usually a small round, black external OL under the terminal cover and it's in the common (120v) wire. Of coarse, it needs to ohm closed. The run cap. is permanently connected between S and R terminals and it's built to take the constant load. If replacing, keep the run cap. Mf within 10% but you can go up on voltage but not down. If you have a start cap. it will also be between S and R but a relay, current type, PTC (positive temperature coefficient) type or potential type is required to open the start cap. circuit when the rotor starts spinning cuz the start cap isn't built to stand an extended load... they will go bang, in short order! An amp clamp is SUPER useful to see what the start winding is doing, on startup. Put the clamp on the start cap circuit and you better see the amps jump and then immediately quit. If that doesn't happen, something is open in that circuit... it's that simple.

So, for the acid test... put your voltmeter on the common and run terminals and you will see the voltage as soon as all controls close and watch the amp clamp to see start currant... it will draw currant if the start cap. and relay are good. Then put the amp clamp on the common wire to see the total amps the comp. is drawing. If all is still going well, move the amp clamp to the run cap. circuit and you can see what the run winding is drawing... and it will be drawing some currant if the run cap. is good
If necessary, use heavy gauge jumpers to bypass the T stat and other controls so you can successfully isolate and check the compressor.

Don't run the compressor very long w/o the fan motor running.

PSC, permanent split capacitor, meaning split phase - a start and a run winding, and the run cap is permanently connected to S and R. The start cap and relay give the rotor an extra kick but the start cap. drops out nearly instantly. IIRC, the start caps on these tiny things are only about 40-50 Mf and are uncommon. If the compressor is cool and been off for a long time, so the pressures are equalized on the top and bottom of the piston, they will usually start w/o the start cap. unless the rotor is sticky.
They're really fast tests, once you've done them a few times.

Something I just found
https://abrwholesalers.com/blog/how-to-check-a-single-phase-compressor/

[sgossman]

Alright I took a break for a day then did some research on how to check the windings and this is what I got on my ohm meter.

Red and White - 5
Black and Red - 4
White and Black - 1

From what I understand this fits the parameters of the windings of sum of 2 lowest equaling the third and the second highest being 2 to 4* higher than the lowest.

[sgossman]

C Schomer wrote:
Diagnosing the compressor is fast. First- check for burnt compressor terminals or burnt O.L. Second- ohm the windings, with cool compressssor, to be sure the internal O.L. is closed.. c-r ohms plus c-s ohms = r-s ohms? If not, kiss the compressor goodbye. Third- There IS a bypass tool called an Annie. Unplug the comp. wires and hook up the Annie, which has manual switches and the capacitors inside, and hit the on and then start button. If it still doesn't start... kiss the compressor goodbye. If it starts, use the volt meter to follow the path to the comp terminals to see whats wrong.
It sound like you know what you're doing. You can do it all with a vom and amp-probe but an Annie makes it fast. I built an Annie in school, mid 70s, for extra points. I bought an Amprobe, vom and a cap. tester as soon as I was out of trade school and they've been indispensable.
Your relay looks like a potential relay and pickup/dropout voltages are critical but who knows what's on these cheap, sh!tty units! Craig

I caught about half of what you said. Everything I learned about capacitors, relays and compressors I learned in the past week working on this AC.

The compressor has a red wire, white wire and black wire connected to it. What do I place where and on what setting to test it for what ever it is i'm looking for?

I checked the leads with wires connected in every combination with the meter on ohms and got a sound on every one.
Should I test the wires this same way while disconnected from the compressor?
The leads on the compressor with wires disconnected?

For further reference my AC looks nearly identical to this one which is what lead me to believe it was the capacitors at first except in my case the fan worked fine.
https://www.youtube.com/watch?v=Ty_ou_TW5EM

[C_Schomer]

Diagnosing the compressor is fast. First- check for burnt compressor terminals or burnt O.L. Second- ohm the windings, with cool compressssor, to be sure the internal O.L. is closed.. c-r ohms plus c-s ohms = r-s ohms? If not, kiss the compressor goodbye. Third- There IS a bypass tool called an Annie. Unplug the comp. wires and hook up the Annie, which has manual switches and the capacitors inside, and hit the on and then start button. If it still doesn't start... kiss the compressor goodbye. If it starts, use the volt meter to follow the path to the comp terminals to see whats wrong.
It sound like you know what you're doing. You can do it all with a vom and amp-probe but an Annie makes it fast. I built an Annie in school, mid 70s, for extra points. I bought an Amprobe, vom and a cap. tester as soon as I was out of trade school and they've been indispensable.
Your relay looks like a potential relay and pickup/dropout voltages are critical but who knows what's on these cheap, sh!tty units! Craig

[sgossman]

Tested the meter and it works fine so I am going to say no, power is not getting to the compressor. This is what I thought originally so I replaced the relay but its a different kind of universal replacement as I laid out earlier in the thread.

[sgossman]

mchero wrote:
Can you see any power at the compressor?

Well when I use this Fluke multi-meter every point I check says "1ac" when set to volts which seems odd. I'm looking for my other multi meter to try that as well.

[mchero]

Can you see any power at the compressor?