OT- Marine air conditioner again.... any theories on what is wrong ?

Cruisair model FS7C. Split system as below link, which is the condenser compressor assembly, except mine is 1993 vintage and uses R22. Size is 7,000 BTU.

https://yachtaidmarine.com/wp-content/uploads/2014/06/R-Series-Condensing-Unit_web_800-500x500.jpg

Symptom is... when the digital display is set for cool, the fan works fine, the "cool" light will come on after a minute. But the compressor will only run a few seconds and then shut down. Then it "rests" for maybe 20 seconds, comes on for a few seconds again, shuts down....will continue this song and dance forever if I let it. (or would have...keep reading...)

I am assuming all this time it is shutting down due to detecting less than 30 psi of R22 but last week I finally got a Marine AC tech over to the boat who did improve my other unit that needed some R22, but this one he seemed surprised the pressure on discharge side was high if anything... like 150 psi.

He thought the problem was a combination of the motor run capacitor and the relay (in his experience whenever a run capacitor goes, it messes up the relay coil) He had neither with him so I said I'd change those out myself.

This weekend I noticed the next larger unit (that works fine) had the exact same relay and capacitors, so I did a switcheroo....put the relay, start and run capacitors from the good unit in the bad unit.... and vice versa. The end result was nothing....the good unit still runs fine and the bad unit still acts exactly the same.

So the tech was wrong.

Fast forward a few days, talk with another marine AC tech who tells me if the "cool" light stays on the digital display when the compressor is not running then the problem is not electronic. He mentions it could be defective thermal overload in the "peckerhead" at the compressor. So find the overload, check continuity and sure enough it does have .004 ohms between it's two terminals when not on.

So I have the bright idea to straight wire this thermal and see what happens. So I do that, and what happens is the compressor sure enough keeps going far longer than ever before. That is, until smoke starts pouring out.... and the start capacitor begins to melt !

Theories as to why this is happening ? Mine are-

1. Compressor has serious mechanical problem that puts it under undue strain.

2. R22 pressure too high (static pressure on discharge side 150 psi) thus putting too much strain on compressor, such that it never gets beyond the start capacitor stage to the run capacitor stage.

3. ?


Thoughts ?

(I realize one problem with theory no. 2 is that one would think it must have run ok at that pressure when it was first charged or the tech would have lowered the pressure right then and there. But who knows.. )

It sounds like a failed start switch on the motor, it stays on the start circuit and over currents. Is the motor separate from the compressor like a vehicle or is the compressor a hermetically sealed unit?

Steve

Steve in SoCal said:

It sounds like a failed start switch on the motor, it stays on the start circuit and over currents. Is the motor separate from the compressor like a vehicle or is the compressor a hermetically sealed unit?

Steve

Click to expand...

compressor is a hermetically sealed unit. I was thinking the motor start switch was in the relay box I did a switcheroo on (if so that is not the problem) but maybe it is somewhere else. Since posting and reading further I'm getting the impression that 150 static discharge pressure is not terribly high for this unit so perhaps that is not it.

I have to assume since the capacitor did a melt down, this is truly a start capacitor only system, where there is a start relay. And the start relay failed closed. This will draw excessive current, and the motor will cycle on the overcurrent protection device.
You have a damn good ohm meter if you can measure 4 milliohms, and this sounds about right for a device that needs to have some resistance for current measuring.

If you have your gauge manifold on this, the pressure on the high and low side should be the same before the compressor starts. I doubt if the compressor can start into a head pressure load.
The 150PSI would be about right for a system that has a charge where it was in a saturated state. This correlates to ~80-85F so the charge is normal, at least in the non running state.

I assume this compressor runs on shore power only.

The only worry you may have is it's possible that you overheated the start winding now, and it may have shorted out some turns if this power was left on too long. Hope the capacitor opened circuit before this happened.

The relay may be a small disk device wired in series with the capacitor. This would be a solid state relay, and is 2 terminals only. I don't know anything about this compressor, so I may be wrong.

It does sound like it was cycling on the OL. Can you post the wiring diagram? Did the compressor actually run or was it just drawing locked rotor? Head pressure should have gone to over 200 and suction to about 75. I would start by checking compressor for grounds, opens,and winding resistance against manufacturer data. because it may have been damaged when you bypassed the OL. If compressor is ok, replace both the cap and the relay.

The cap was probably stressed from all the starting. If it's cap start cap run one of them is in the circuit the entire time. Need to check run current, to make sure compressor is within specs there. Also if it is 220 and single phasing that can cause problems also.

Maybe this will help..Cruisair model FS7C http://www.flightsystems.com/pdf/cruisair-troubleshooting-guide.pdf

If memory serves me right , (this is on older units )there is a bypass valve between the high and low sides to bypass the coil. This is so the cooling water is not working the compressor doesn't rotor lock and burn up, it just cycles the Freon beck o the low side. If this valve gets stuck , no cooling. If it gets stuck in the between bypass the compressor go's into rotor lock immediately and pops the pecker head breaker.

The potential relay senses current and voltage , like on a RPC . If this gets out of wack , then the compressor starts funny or try's to start , burning up the cap.

On those units were Copland or tchumcie compressors. I usually went to home depot and bought a window shaker and used the scroll compressor as a swap out , cheap and dirty but works better than the CA comp..

I usually just do RV units now and have the same issues.

Just the other day I heard a story about an old and experienced A/C tech who would always use a meter to check the load on the motor while charging a system, and stop when the meter showed the rated load. Based on that story, I'm going with your system is overcharged.

charlie gary said:

Just the other day I heard a story about an old and experienced A/C tech who would always use a meter to check the load on the motor while charging a system, and stop when the meter showed the rated load. Based on that story, I'm going with your system is overcharged.

Click to expand...

Yes good advice , usually I'll do a check for FLA after a cap and relay replacement and check for low voltage or voltage drop in the feed lines. Motorcoaches are subject to bad plug connections or burnt plugs connections.

Usually on those units, repeated cycling means the unit is tripping out on either high or low pressure. The caveat is that usually it tries just 3 times then the display changes to HPF or LPF (or similar) and stops.

In your case, if the compressor actually started, I would expect to see the discharge pressure drop to 55-60psi, but maybe it didn't run long enough to achieve this?

You'll probably find the unit has two capacitors - a start and a run. If you smoked the start cap, you probably inadvertently bypassed the start relay and kept the start windings hot the whole time.

My suggestions from here are to start with the basics. Remove the wires from the hermetic compressor and measure the resistances.
C-R should be a few ohms.
C-S should be a few ohms more
Case to C, R or S should have no continuity.
If you can, check the amp draw when it's running and make sure it doesn't exceed to nameplate. There would be no reason for the thermal to trip if the amp draw is good.

Hi & Lo pressure switches can be bypassed (jumpered) for testing purposes if necessary, but don't forget to hook them up again.

If all else fails, you can bypass the entire electronics board and rub the hermetic compressor using a run cap, some switches and a start cap to simulate the start relay. Such a device is called an "Annie". I use mine quite a lot for this very purpose.

I'm not an A/C tech. But sometimes the problem isn't electrical.. All of the above seem to be
sure it is.. The filter/dryer may be plugged..
Have You had the expansion valve checked?? The compressor will short cycle from high pressure
if the Freon can't get to the evaporator..


Good Luck

Sauerkraut said:

Have You had the expansion valve checked??

Click to expand...

No...where is it and how to check it ?

You might want to ask Your A/C tech about this before starting..

It should be in the hi pressure line after the filter/dryer and just before the evaporator..
in the same housing as the evaporator..
It will have a capillary tube that also goes to the evaporator.. I don't know if this is the correct
way to test? But its the only way I know without pumping out the system and unsoldering the valve..

Start the system and touch the main line after the valve to check if it is cooling if not..
Carefully remove capillary line from evaporator wrap Your hand around the end of it to warm it up..
Start system up touch main line to evaporator line should get cold.. If not valve isn't working
or filter/dryer or line is plugged..

Like I said before I'm not an A/C tech, just worked on My own stuff back in the day..

I hope this helps
Steve

Was waiting patiently for a wiring diagram. If not available can you open up the control cabinet and take a pic. Also one of the peckerhead opened if possible.

JR

Milacron said:

No...where is it and how to check it ?

Click to expand...

You really need a set of gauges and a thermometer. The temperature of the suction line should be some number of degrees above the evaporation temperature of the refrigerant, this is called superheat. Old school rule of thumb was 12 deg but unit specs differ. Some TX valves are adjustable others are not. If you do infact have one it will be on the evap coil inside the blower section. Pressure temperature chart below.



So say your suction pressure is 60# that means the temp it is evaporating at is about 34 deg. So with a 12 deg superheat your return temp should be about 46 deg. Bulb placement for the TXV is important and should be like this.



The bulb and pipe should be insulated.

JR

I don't think the TVX is your problem UNLESS for some reason the system pressures are not equalizing when it is off and one of the techs should have seen that. Unless, of course, they were bewbs

A 7000 BTU system is going to be a cap tube system not a TXV. Even if the cap tube were clogged, the compressor would still kick off electrically when the lo pressure switch opened.

Most likely true (although look at Danfoss for low capacity TX valves or Sporlan for that matter, they do exist), but in any case like I said "I don't think the TVX is your problem UNLESS for some reason the system pressures are not equalizing when it is off" I don't think refrigerant metering is his problem. Either the compressor is bad, or something is up with the start relay / capacitor if it has one, (no wiring diagram)or there are bad / corroded wiring terminals or even low voltage from a bad breaker or bad connection on the line side (unless the system is not equalizing). It could even be a closed service valve if someone screwed up. Nobody has even measured start amps. Did the tech check how the refrigerant smelled? If the compressor went toasty that is a dead giveaway. You mentioned the high side rose to 150 PSI, which is not at all high. What was the low side pressure?

JR

Is one of these in this PDF , your model ? http://www.dometic.com/QBankFiles3/...nditioning/L-0884-AH-Wiring-Diagrams_6147.pdf

emcmike said:

Is one of these in this PDF , your model ? http://www.dometic.com/QBankFiles3/...nditioning/L-0884-AH-Wiring-Diagrams_6147.pdf

Click to expand...

Here's the wiring diagram from the condenser/compressor

Being all the electrical systems intact and working , as You said " did the switcheroo " and things were the same.
I believe that the cooling pump went down and the compressor did not shut down , wich is not unusual being someone had it wired differently.
This causing the compressor to run hot and some flaking took place inside the sealed unit. This in turn has plugged up the capillaries tube causing the high pressure and shut down. I'm sure if you cut the tubing and blow it out in a white sock, you'll see the flaked parts.