Grunert Refridgeration

I have a Grunert 12 volt “Polar Mate” refrigeration unit that works well...when it works. I have noticed some pretty dramatic temperature fluctuations over the summer but the unit was always working well when I checked things. Last evening I found melted ice cubes in the freezer and a cool box. Unit not running. Quickly checked for power and had 12 volts at the supply connection, jumped the thermostat but the compressor still didn’t start. I ohmed out the thermostat and found the circuit closed as it should be when calling for the compressor to start.
Last resort I tapped the mounting plate with a hammer and it started right away. Seems to me that it narrows down to a loose connection, faulty start relay, or faulty compressor. Any thoughts or Past experience would be appreciated.

Is there a start capacitor? Do you have a model number or schematic?

Bud said:

Is there a start capacitor? Do you have a model number or schematic?

Click to expand...

schematics. Model PMEAW08

Cigatoo said:

schematics. Model PMEAW08

Click to expand...

There should be another schematic showing compresor and condensor unit. Next time it does not start check voltage at compressor. then work back to source. Should go through an overload protect, relay. a high pressure switch and sometimes a low pressure switch. As you check voltages you can inspect for loose connections.

Thanks

Bud
Thanks so much for that info. Will check this weekend. Downloaded schematic from the web. Will look further. Greatly appreciated

Bud said:

There should be another schematic showing compresor and condensor unit. Next time it does not start check voltage at compressor. then work back to source. Should go through an overload protect, relay. a high pressure switch and sometimes a low pressure switch. As you check voltages you can inspect for loose connections.

Click to expand...

It's a Danfoss compressor with SECOP module. Conventional compressor troubleshooting doesn't apply.


The 1st step in DX the module would be installing an LED between (+) and "D". It will give you an error code if the module is tripping. Instructions along with error code keys are easy to find on SECOP's website, and myriad other sources on the web. These modules are very intolerant of low voltage, so check the voltage with a DMM at the (+) / (-) terminals on the module while the unit is operating. Checking static voltage is not conclusive. Anything under 12.0 VDC can create a problem. Power wiring should be liberally sized, you can't go too big, too small is typical. Size for minimal voltage drop ~1%.

A flakey thermostat that chatters can easily make the compressor start/stop/start, this will create an error condition.

The LED will tell you why it's shutting down. Modules run around $300, depending, and they are not particularly robust. Older vintage were sensitive to temperature problems, they would cook themselves. The hammer DX was more likely a fluke.

Maerin said:

It's a Danfoss compressor with SECOP module. Conventional compressor troubleshooting doesn't apply.


The 1st step in DX the module would be installing an LED between (+) and "D". It will give you an error code if the module is tripping. Instructions along with error code keys are easy to find on SECOP's website, and myriad other sources on the web. These modules are very intolerant of low voltage, so check the voltage with a DMM at the (+) / (-) terminals on the module while the unit is operating. Checking static voltage is not conclusive. Anything under 12.0 VDC can create a problem. Power wiring should be liberally sized, you can't go too big, too small is typical. Size for minimal voltage drop ~1%.

A flakey thermostat that chatters can easily make the compressor start/stop/start, this will create an error condition.

The LED will tell you why it's shutting down. Modules run around $300, depending, and they are not particularly robust. Older vintage were sensitive to temperature problems, they would cook themselves. The hammer DX was more likely a fluke.

Click to expand...

Steve
Thank you. Spoke with a local service guy today. As I was advised here they said the problem sounds like low voltage. Will check all connections with a meter over the weekend.
Thanks again.

Cigatoo said:

Steve

Thank you. Spoke with a local service guy today. As I was advised here they said the problem sounds like low voltage. Will check all connections with a meter over the weekend.

Thanks again.

Click to expand...

Don’t overlook wire size.

"Don’t overlook wire size."


One case where bigger IS better.

Maerin said:

Don’t overlook wire size.

Click to expand...

Wiring is good. Boat is wired correctly. Was lucky the compressor was acting up when I got to boat (starting and stopping) had 12.6 volts at the compressor. Started wiggling things and found something that looks like Sa fuse holder on the back of one of the terminals where the thermostat connects to the compressor unit. Not sure what it is yet. Hard to see. When I wiggled it compressor started and has run correctly since. Need to investigate further. Maybe corrosion or loose connection? We shall see. Enjoying perfect late summer weather right now

"Maybe corrosion or loose connection?"

Take a tip from GM bus co and install a star washer under every round terminal end , after cleaning.

The star washer will allow the terminal eye to heat and cool when in use , and still remain with good pressure contact , that keeps the current flowing.

A box or two of 100 is cheap insurance . Copper is best conductor,

https://www.bokers.com/star_washers.asp

Cigatoo said:

Started wiggling things and found something that looks like Sa fuse holder on the back of one of the terminals where the thermostat connects to the compressor unit. Not sure what it is yet. Hard to see. When I wiggled it compressor started and has run correctly since.

Click to expand...

A loose connection in the thermostat circuit - as well as a thermostat that's chattering can easily create problems. It causes the compressor to start/stop/start, and that will cause it to lock out on a high starting current fault. The module will lock out for a time, and the diagnostic LED will flash 3X....3X....3X... during that period. It will self-reset and try again. It will also tell you if there's a problem with voltage, among other things. The LED will tell the tale, and is the 1st step in DX any problem with the Danfos/SECOP module, as noted in post #7. Without it, you're guessing. You can post symptoms to the forum, then you get six guys all guessing.



Here's a good explanation of the LED use by Coastal Climate Control. They will sell you the LED, you can make one up with a loose LED and resistor if you've got the materials on hand. Start with that and find the problem.

It appears that the thing that looked like a fuse is actually a 1500 ohm resistor for the thermostat according to the schematic. Since I wiggled the resistor the system has been working fine. (Always better to be lucky then good) I need to move some ac ducting to get a better look. Hoping that is is just a poor connection. Pic of schematic and pic of the component (black thing) if anyone is interested.

The resistor sets the compressor speed.

There are several optional controllers that can be used on the SECOP modules that optimize the compressor speed for load, most include the "D" connection to provide the fault codes. You can leave the LED permanently attached to the "D"-"+" terminals, so if you suspect a problem, it's easy to see if the module's returning a fault code.

Maerin said:

The resistor sets the compressor speed.

There are several optional controllers that can be used on the SECOP modules that optimize the compressor speed for load, most include the "D" connection to provide the fault codes. You can leave the LED permanently attached to the "D"-"+" terminals, so if you suspect a problem, it's easy to see if the module's returning a fault code.

Click to expand...

This (Polar Mate) unit has a blue LED built into it next to the fuse. There were no fault codes / blinking lights.

Most of the codes will self-reset, so unless you catch it in the act, you could easily miss a fault code.



You can test the LED by removing the "D" terminal from the module and temporarily connecting it to the (-) ground. The LED should light.


A 3 flash code isn't unusual, a loose connection in the thermostat circuit can cause it, a failing box thermostat can also chatter and cause it to fault out. Hope you can find some reason for the problem. Intermittent stuff is the pits.

Maerin said:

The resistor sets the compressor speed.

There are several optional controllers that can be used on the SECOP modules that optimize the compressor speed for load, most include the "D" connection to provide the fault codes. You can leave the LED permanently attached to the "D"-"+" terminals, so if you suspect a problem, it's easy to see if the module's returning a fault code.

Click to expand...

Steve thanks for your input. It is greatly appreciated. When installing an optional controller would I eliminate the 1500 ohm resistor?

If it has a speed control function, then the resistor isn't needed. I added a Merlin II speed controller, and that replaces the resistor since it varies the resistance in the T-C circuit to control the compressor speed. The Merlin also includes the fault LED that is wired to "D". It's made to piggyback onto the module's terminal connectors, but won't fit the newer ones that the spacing's changed. It can still be used, but it must be connected with jumper wires and then attached somewhere. I just wire tied it to the wiring to keep it away from any conducting metal. It does seem to help, it also enables the compressor to run full speed to help in high load conditions.