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#1
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A/C fan runs, no compressor
The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. There is no (apparant to me) low-pressure cutoff switch on the unit. When the thermostat calls for cooling, the fan runs but not the compressor, even after it has rested for 24 hours. The A/C ran last summer. I just bought the house last year so I don't know the history of the unit or its maintenance. I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure.
There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals. The resistance between the C and R terminals is 2 ohms. The resistance across the S - R terminals (and the run cap) is between 1-4 megohms. I take it this means my run cap is not shorted. Based on the high resistance, is the S terminal open or the S coil burned up? I have not measure the voltage to the compressor while the relay is engaged, so one of the relay contacts may be bad...but I thought I would try some meter probing first... Gado |
#2
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"gado" wrote in message ... The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. There is no (apparant to me) low-pressure cutoff switch on the unit. When the thermostat calls for cooling, the fan runs but not the compressor, even after it has rested for 24 hours. The A/C ran last summer. I just bought the house last year so I don't know the history of the unit or its maintenance. I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure. There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals. The resistor is not a heater, but a bleed down resistor. It's there to hopefully keep people from getting hurt. |
#3
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"gado" wrote The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. Do you mean single phase 208 or 240? |
#4
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"gado" wrote in message ... The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. There is no (apparant to me) low-pressure cutoff switch on the unit. When the thermostat calls for cooling, the fan runs but not the compressor, even after it has rested for 24 hours. The A/C ran last summer. I just bought the house last year so I don't know the history of the unit or its maintenance. I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure. There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals. The resistance between the C and R terminals is 2 ohms. The resistance across the S - R terminals (and the run cap) is between 1-4 megohms. I take it this means my run cap is not shorted. Based on the high resistance, is the S terminal open or the S coil burned up? I have not measure the voltage to the compressor while the relay is engaged, so one of the relay contacts may be bad...but I thought I would try some meter probing first... Maybe bugs or other crud in the compressor contactor, since its been sitting for so long. Pull the your mains disconnect at the condensor unit and jumper "Y" to "R" a few times in order to shuttle the magnetics...your relay solenoids will still work work because the 24 vac control voltage comes from your air handler transformer.....after that, suggest maybe blow any debris out of the contactor with compressed air, if available. If the capacitor is suspect, usually best to just replace it with a new one. -- SVL |
#5
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gado wrote:
snipped I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure. Tsk, tsk, now that you've told the world what you did...Expect a visit from the global warming nazis swithin a couple of days. G There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals. The resistance between the C and R terminals is 2 ohms. The resistance across the S - R terminals (and the run cap) is between 1-4 megohms. I take it this means my run cap is not shorted. Based on the high resistance, is the S terminal open or the S coil burned up? It sure looks that way. The other end of the start winding ought to be connected to the C terminal, so you should have seen a low resistance between S and R, (the sum of the start and run windings) regardless of what else may be tied in parallel. I have not measure the voltage to the compressor while the relay is engaged, so one of the relay contacts may be bad...but I thought I would try some meter probing first... Go ahead and try that. If it's a dirt simple unit the fan motor is being switched on by the same relay as the compressor, so the relay's probably doing it's thing and I bet you'll find voltage going the the compressor too, stymied by an open start winding. Let us know what it turns out to be. Jeff Gado -- Jeffry Wisnia (W1BSV + Brass Rat '57 EE) "Truth exists; only falsehood has to be invented." |
#6
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"gado" wrote in message ... The outside A/C condensor unit (Trane TTJ type) of my home has a CSR-type compressor. It has two phase 120VAC fed to it. There is no (apparant to me) low-pressure cutoff switch on the unit. When the thermostat calls for cooling, the fan runs but not the compressor, even after it has rested for 24 hours. The A/C ran last summer. I just bought the house last year so I don't know the history of the unit or its maintenance. I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure. There is a run capacitor across the S and R terminals of the compressor. The electrical schematic diagram of the compressor shows a resistor (heater?) between the electrical coils of the S and R terminals. The resistance between the C and R terminals is 2 ohms. The resistance across the S - R terminals (and the run cap) is between 1-4 megohms. I take it this means my run cap is not shorted. Based on the high resistance, is the S terminal open or the S coil burned up? I have not measure the voltage to the compressor while the relay is engaged, so one of the relay contacts may be bad...but I thought I would try some meter probing first... Gado This is Turtle. If you have 1-4 megohms between S and R of the compressor terminals, It is looking like a burnt start winding in the compressor. now to be sure remove wires from the compressor and read across C and S on compressor terminal and if you don't get a normal OHM reading like less than 100 and get Megohms, You compressor start winding is burn if you get the megohms reading or none. TURTLE |
#7
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Large numbers of global warming nazis, probably driving black Hummers which
get 2 MPG and don't have catalytic converters? -- Christopher A. Young Learn more about Jesus www.lds.org www.mormons.com "Jeff Wisnia" wrote in message ... gado wrote: snipped I took the cap off the freon return line and pressed the valve, there is at least some freon in the system but I don't have gauges to see how much pressure. Tsk, tsk, now that you've told the world what you did...Expect a visit from the global warming nazis swithin a couple of days. G |
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