06-18-2015, 07:49 AM
The amps on the compressor in question is 4.6 at start-up and drops to 4.0 within a minute or so. A comparable compressor starts at 8.6, drops to 6.9 in about a minute, and then gradually rises to 11 over the course of the next 5 minutes before stabilizing. The amps used by the compressor in question suggest low flow through it.
The superheat: with suction at -2.7psi R22 boils at -45 degrees, temperature of the input pipe at the compressor was 67 degrees (essentially equal to ambient temperature), therefore the superheat would calculate to 112 degrees which is far away from the generally accepted ideal of 5 degrees and is an indication of very low flow of refrigerant through the system.
Subcooling: with the boiling point of R22 at 67 degrees being approximately 130psi and the bottom of the condenser being 67 degrees there is no subcooling seeming to occur. This too seems to indicate very low flow through the system.
All these data points are consistent in pointing to very low the flow through the system. The question to be answered is whether this is due to low charge or a big restriction in the system. I'm in agreement with the tech and his boss that the most likely cause is a restriction due to the following logic; the liquid pressure is what is expected given the ambient temperature while the suction pressure is -2.7 when it would more commonly be expected 60psi or so.
I may have to rebuild the system anyway. A compressor that has run for a long time with low/no flow can easily get messed up internally though given the vacuum it's pulling it does seem to pump. However, there is a strange rattle that could be only due to the low flow or it could portend future failure. I've got to place a bet one way or the other. Either way this is an interesting challenge and a great distraction from the other issues in my life.
Now, I, the tech, and his boss could all be wrong. If you see blind spots in the logic I've presented I would appreciate any additional thoughts. I'm beginning to think that, given the number of systems in the coach, I should buy all the tools, get sufficient training to be certified so I can buy the refrigerant, and do my own work. Tool drool occurring NOW!
The superheat: with suction at -2.7psi R22 boils at -45 degrees, temperature of the input pipe at the compressor was 67 degrees (essentially equal to ambient temperature), therefore the superheat would calculate to 112 degrees which is far away from the generally accepted ideal of 5 degrees and is an indication of very low flow of refrigerant through the system.
Subcooling: with the boiling point of R22 at 67 degrees being approximately 130psi and the bottom of the condenser being 67 degrees there is no subcooling seeming to occur. This too seems to indicate very low flow through the system.
All these data points are consistent in pointing to very low the flow through the system. The question to be answered is whether this is due to low charge or a big restriction in the system. I'm in agreement with the tech and his boss that the most likely cause is a restriction due to the following logic; the liquid pressure is what is expected given the ambient temperature while the suction pressure is -2.7 when it would more commonly be expected 60psi or so.
I may have to rebuild the system anyway. A compressor that has run for a long time with low/no flow can easily get messed up internally though given the vacuum it's pulling it does seem to pump. However, there is a strange rattle that could be only due to the low flow or it could portend future failure. I've got to place a bet one way or the other. Either way this is an interesting challenge and a great distraction from the other issues in my life.
Now, I, the tech, and his boss could all be wrong. If you see blind spots in the logic I've presented I would appreciate any additional thoughts. I'm beginning to think that, given the number of systems in the coach, I should buy all the tools, get sufficient training to be certified so I can buy the refrigerant, and do my own work. Tool drool occurring NOW!
Jon Kabbe
1993 coach 337 with Civic towed