Compressor Not Running but Cond Fan Is. Is My List of Possibilites Complete?

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Old 07-13-17, 01:55 PM
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Compressor Not Running but Cond Fan Is. Is My List of Possibilites Complete?

I have an old Carrier split system where the compressor is not running with the following facts:

* The condenser fan is running fine
* It's getting 24 volts to the pressure switch (contactor)
* I got 240 volts on all wires after the pressure switch (contactor)
* I got 240 volts at the compressor's wire connector itself
* The compressor wires and all other wires look good
* The capacitor looks new and shiny and the top is still flat; I think I replaced it 2 years ago.

So far I have 3 possible causes:
(1) Bad capacitor
(2) Low Freon/R-22 (assuming low Freon lets the fan run)
(3) Bad compressor

Are there any other possibilities? I'm going to get a new capacitor tomorrow and then be forced to call a technician (which I want to avoid).

Thanks!!
-Tony
 
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Old 07-13-17, 02:07 PM
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Tony, since the condenser fan is running, you have 24VAC at the outside unit and the contactor is working. If your unit has a low pressure switch (not all do), it would open the 24V signal going to the contactor meaning that neither the compressor nor condenser fan would run.

By all means try a new capacitor, as that's relatively inexpensive and could cause the symptoms you're seeing. If that doesn't solve the problem, turn off the power to the outside unit (check with a voltmeter to make sure power is off) and check the electrical connection where the compressor power cable plugs into the compressor. In the past, some people have reported (and shown pictures) of one or more terminals being burned up due to a poor connection causing the terminal to get hot and burn up. While you have the cable off, check resistance between the 3 compressor terminals (1-2, 1-3, 2-3).
 
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Old 07-13-17, 02:11 PM
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Agree with Bob14525...............................
 
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Old 07-13-17, 02:49 PM
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Thanks for the reply!

Yes, I did pull the 240 volt wires off the compressor and they all look very good and clean. I once had one of those block terminals burn off (on a different system), so I knew to look there too.

If I do check the resistance on 1-2, 1-3, and 2-3, what measurements am I looking for?

Thanks again!

P.S. Will low freon stop the compressor but let the fan run? (maybe thats what you meant about the low pressure switch)
 
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Old 07-13-17, 03:01 PM
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You have solely a compressor issue.

If the fan is running.... 24vac is good. 240vac is good. Contactor is good. Pressure switch good.
 
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Old 07-13-17, 03:11 PM
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Uh, Oh. I used the wrong term in my original post. I said "pressure switch" when I mean "contactor."

I did not check the pressure switch if it has one. I'm not sure what it looks like, but I'm guessing it'll feed off the copper tubing and have wires going to it to cut off the flow of electricity.

Sorry!

I'm still wondering if low freon will allow the fan to run like mine is.
 
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Old 07-13-17, 04:13 PM
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Can't make it much clearer than this......

If the fan is running.... 24vac is good. 240vac is good. Contactor is good. Pressure switch good.

If the pressure switch is good then you DO NOT have a low refrigerant problem.

You have solely a compressor issue.
A wire broken from the contactor to the compressor or starting cap.
A defective cap.
A defective compressor or wiring connections AT the compressor.

A little more far flung.... someone bypassed the low pressure safety switch, the refrigerant all leaked out and the compressor is now shot.

If you check resistances at the compressor.... there should be a reading between all three terminals. 1-2, 1-3 and 2-3.
 
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Old 07-13-17, 06:36 PM
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PJ: OK, I didn't understand your previous post, but now I do. Plus I totally missed Bob's sentence: " If your unit has a low pressure switch (not all do), it would open the 24V signal going to the contactor meaning that neither the compressor nor condenser fan would run..." which explains it ...sorry! For some reason I was thinking that the low pressure switch was 110/220 volt, but since it's 24V, that makes sense that both the fan AND compressor would not run since they both are wired to that 24V contactor.

Could a bad capacitor run the fan, but not get the compressor started? I was figuring on getting a new capacitor tomorrow morning but I'd surely skip it if it can't be the problem.

Thanks again!!
 
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Old 07-13-17, 07:42 PM
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Yes... a bad cap could run the fan and not the compressor.

Usually in that case the compressor will short cycle and hum loudly since it can't start. It would also be red hot since it would be cycling on thermal overload.

Leave the system off and try the cap first.
 
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Old 07-13-17, 07:55 PM
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Yes, the Herm side of a dual cap can fail while the Fan side of the cap is still within specs.

PJ you are too fast for me.
 
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Old 07-14-17, 10:14 AM
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FIXED! It was the capacitor.

I tested the 3 terminals on the compressor for ohms and one was stable and the other 2 just jumped around like crazy and never would settle on a number.

I figured I'd just buy the capacitor and when I did, I hooked up the wire to the compressor only on the capacitor and pushed in the contactor and the compressor ran!

Thanks for everyone's input; I learned a lot on this one!!

-Tony

P.S. I just paid a technician $500 to simply have a system charged with R22 prompting me to possible getting my cert to handle R22 and I learned how to charge with a TPX valve with subcooling. But I swear my outdoor unit's plate say 20 degrees F ...anyone ever heard of 20F subcooling? That seems like a lot; aren't most 12 degrees F?

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Last edited by tony17112acst; 07-14-17 at 12:00 PM.
 

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