SCS A/C Compressor running without evaporator blower - Printable Version

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+--- Thread: SCS A/C Compressor running without evaporator blower (/showthread.php?tid=4311)

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SCS A/C Compressor running without evaporator blower - pestes - 06-20-2018

Yesterday, we had our front SCS air freeze up on us. Not sure how long it was frozen for but before I realized what had happened, I had flipped thermostat controls around in various ways (Hi/Lo, just fan, etc). Once I realized that with just the fan on, I was getting no air flow, it had become apparent that it was a freeze up.

I cleaned the filters under the stairs and then I ran the evap fan for a while to help the melt and then turned the thermostat to Off before heading to bed.

About 10 minutes later, the wife noticed that the A/C compressor on that unit was running. Even though the thermostat was in the Off position. And the evap blower was not running.

If I turned the therm back to Cool, the evap blower would come on. Turned back to off and the blower stopped but the compressor kept running.

I turned the thermostat back to cool, set it to a set point just above the current temp, and after a minute or two, the whole thing turned off as one would expect.


So I figured that the thermostat is going wonky on me.

However........

It was late, so I killed the breakers for that unit and went to bed again.

Then the wife notices that even though the rear air evap blower is not running, the rear compressor is!

Same story as the front - I set the set point to just above current temp, waited a bit, and it turned off.

I can't believe that I've had 2 thermostats fail in the same fashion on the same day. Or at least near enough to each other that it seems like they failed on the same day.

Is there any reason whatsoever that the compressor should ever be running without the evap blower? To me that seems like a sure fire way to have a freeze up, and I suspect it is why my front unit froze in the first place.

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RE: SCS A/C Compressor running without evaporator blower - Richard - 06-20-2018

Short answer is NO. Something wacky is going on. Are you plugged into a new pedestal? If so, unplug and see if the same thing happens on generator.

Have you installed external relays for the compressors?

It is possible that you had some power event that welded the contacts in the compressor relays. Read the schematic on the circuit board, and unplug the leads to the compressor. Ohm the connection to power in block. All of this with power off of course. If the voltmeter shows a path from the connection to the power block with power and tstat off, then the relay is the culprit

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Call me 817 223 2056 if you need to

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RE: SCS A/C Compressor running without evaporator blower - pestes - 06-20-2018

Thanks, Richard. "No" was pretty much my expectation.

We arrived here on Saturday, so we've been here a few days thus far. We've got a new pedestal about every week. I do have a Progressive EMS with no faults on this pedestal.

I have the relays, but I never got a chance to do the job before hitting the road and haven't taken the time to do it while on the road.

I am certain, however, on both units that the signal was being triggered from the thermostat, and not a stuck relay on the control board. At least, unless there are 2 signals that must be present from the control board. I'm trying to think back to what made me come to that conclusion last night. I believe it was because if I switched the thermostat to Heat -- the compressor went off. Switched it back to Off and the compressor came on.

Also, just to be clear, my statement of "the compressor was running" means that the unit was making noise but the evap blower was not running. I would presume that the thermostat does not control the condenser fan and compressor separately, that a single signal from the thermostat will trigger both. The logic table in the SCS documentation seems to confirm that - Relays 5, triggered by Y1 from the thermostat powers both Compressor 1 and the Low side of the condenser fan, with Y2 driving Relay 5 and thus Comp 2 and the High side fan.

It's been running ok today, although it has been warm enough that it has not stopped running. I am fearing low freon levels may be an issue as it's only been in the mid 80's here today. I need to see if I packed the clamp meter to check current on the compressors.

If I can get the compressor running, evap fan not running state again, I'll pull out the multimeter to get a better look. Bed time was an unfortunate time for this to start acting up last night.

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RE: SCS A/C Compressor running without evaporator blower - pestes - 06-20-2018

Side questions:
1. The 11A - 12A for the compressor -- is that on the mains input that comes into the board on top or bottom (ie compressor + evap blower + condenser blower)? Or do I need to get just the compressor wire out of the bundle?
2. One thing that's always been annoying: If I switch the thermostat to Off, then both the heat and cool setpoints get reset to ridiculous values. Is that normal?

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RE: SCS A/C Compressor running without evaporator blower - Richard - 06-20-2018

The 11 to 13 amps is for compressor only. Since the evap and cond fans are
powered from leg one, measuring the mains will give you about 15 or so on one leg and 12 on the other . Clamp the meter in the compressor wires only to see what it is pulling


And yes turning the tstat to another setting such as off or heat resets the temp setpoints

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