Preface 1

Safety Considerations 2

How It Works 2

Operation 3

Maintenance 4-5

Trouble Shooting 6

Manufacturers Limited Warranty Agreement 7

Worldwide Service Network 1997 8-9



Congratulations on the purchase of your Grunert refrigeration holdover system. No matter which of the following features was the reason you purchased this system, we are sure it will meet your needs and will give you many years of efficient and trouble free use.

The Grunert refrigeration holdover plates are designed to provide consistent temperatures throughout the holdover period. These units are available in HP through 2HP capacities and voltages of 115 or 230VAC at 50/60 hertz (1HP and above available in 230VAC only) and 12, 24 & 32VDC. These units are designed for marine applications incorporating the following features:

Initially, the proper thermostat setting will need to be determined. Turn the thermostat clockwise to its highest (coldest) setting. Monitor the plate surface temperature until it has reached 5F below its eutectic temperature. Once this temperature has been achieved, slowly turn the thermostat back (counterclockwise) until the condensing unit cycles off. The thermostat has an 8F differential, therefore, the condenser should cycle back on when the plate temperature is 3F above its eutectic temperature. If this does not occur, slowly raise the thermostat setting (lowering the temperature) until the condenser cycles on. Note the final thermostat setting so that it can be readjusted should the set point be changed. Normally the thermostat will call the system on for short intervals throughout the day to continually restore the full BTU capacity of each plate. Setting the thermostat lower than recommended will only cause the system to work harder, the plate may get a little colder but will quickly return to its eutectic temperature once the condenser cycles off. The box temperature should average between 5-15F above plate temperature.

On occasion, the holdover plate will get a solid covering of frost which will insulate the internal plate temperature from the box with a 32F ice barrier. If the ice barrier exceeds " thickness it will be necessary to defrost the plate. This can be accomplished by turning the power to the holdover plate system off and then pouring hot water over the plate or with the use of a portable hair dryer. An ice pick, metal scraper or any other metal instrument should not be used as it may puncture or damage the plate surface. Once the plate has been defrosted and the box has been cleaned and drained of excess water, and before operating the system, plug the drain hole(s) to prevent any bilge fumes from getting into the box.

Generally, refrigerator foods should not be in contact with the surface of the holdover plate because of the potential for freezing the food.


Sea Water Strainer

Insure that your pump receives adequate sea water flow by regularly cleaning the strainer basket. Failure to utilize and maintain a proper seawater strainer will void the system warranty.

DC Voltage Pumps

The brushes and springs on the electric pump motor must be maintained. Replace any brushes that are less than of their original length. Replace weak springs. It is recommended to check and replace, as needed, the brushes and springs before any extended voyage. It is also recommended to keep an extra set of brushes and springs on board. The brushes can be accessed by removing the two screws on either side of the end of the pump. Brushes should slide freely in their slots, if not, thin the brushes using sandpaper.

Air Cooled Systems

Use a soft bristle brush to clean aluminum fins on the condenser coil to remove any debris, brushing in the direction of the fins. Flush with a fresh water hose as needed. Lubricate the fan motor with three drop of "3 IN 1" oil annually or as indicated on motor.

Water Cooled Systems

Back-flush condenser coil with a fresh water hose periodically. Use a 5% muriatic acid solution to remove scales from the inside walls of the condenser coil as needed.

Belt Driven Models

Check the belt for cracks and wear. Also check the tension of the belt. The belt should have between " and " deflection from a straight line between pulleys. The brushes and springs on the electric motor must be maintained. Replace any brushes that are less than of their original length. Replace weak springs. It is recommended to check and replace, as needed, the brushes and springs before any extended voyage. It is also recommended to keep an extra set of brushes and springs on board. The brushes can be accessed by removing the cover plates on either side of the electric motor. Brushes should slide freely in their slots, if not, thin the brushes using sandpaper.

All Systems

Spray a light coat of mineral oil onto all painted surfaces to help prevent corrosion being careful not to get oil on the belts or pulleys of belt driven models. If the unit is subject to extremely damp conditions, clean and spray paint as required to prevent rust.



There are several methods of winterization, some of which work better than others. The four various methods employed using a 50/50 non-polluting biodegradable anti-freeze/water solution are:

1. Pumping of anti-freeze solution into the overboard thru-hull fitting, and discharging through the intake thru-hull fitting. 2. Use of the sea water pump to pump anti-freeze solution through the system and discharging through the overboard thru-hull fitting. Close sea cock, remove hose from strainer discharge, raise hose above pump (so pump does not lose its prime) and pour in anti-freeze solution. Pump solution through system. The strainer and hose to sea cock will also need to be drained of water.

3. Use of pressurized air injected at the overboard discharge fitting and the water being discharged through the sea water intake fitting.

4. Use of pressurized air to force water to be discharged through the overboard thru-hull fitting.

Note: Collect all discharged liquids and recycle or dispose of in a proper manner.

Any method which causes the anti-freeze solution to flow downward is the best method of choice. By this means, the anti-freeze solution will displace any water trapped and eliminate the possibility of freezing in hidden areas. In addition, since the sea water pump utilizes a magnetically driven impeller, the impeller should be removed from the wet end assembly, wiped with an alcohol solution, and stored in a warm, dry area until commissioning.



System will not start.

System runs for short time then cuts off.

System runs continuously.


Circuit breaker is off.

Input line voltage is insufficient.

Thermostat is not calling for the system to operate.

Oil pressure switch is open (optional component).

Electrical box circuit breaker tripped or fuse blown.

High pressure switch open.

Low pressure switch open (optional component).

Thermostat set point temperatures are improperly selected.

Thermostat sensing bulb dislodged from well.


Turn circuit breaker on at ships panel, check breaker on unit electrical box.

Check power source (shore/generator) for proper voltage. Check wiring and terminals for proper sizes and connections.

Readjust thermostat remembering that the thermostat does not control the box temperature, it controls the plate temperature.

Check engine oil pressure.

Disconnect AC & DC power supplies to box and check for loose connections. Change fuse/reset breaker. If it blows/trips again, call your local authorized service technician.*

Check sea water flow; clean strainer and/or thru hull intake, inspect sea water hoses for kinks or obstructions, verify that pump is working (check circuit breaker).

Thermostat setting is to low - unit running longer than necessary.

Call for service technician to check system pressures.*

Check temperature set-point, adjust as necessary

Reinstall sensing bulb and use caution when loading box.*NOTE: Marine refrigeration systems are complicated and sensitive pieces of equipment. Many potential problems and their solutions are beyond the scope of this manual. For the nearest certified refrigeration mechanic, see the Worldwide Service Network at the end of this manual.


The following warranty is extended to cover products manufactured or supplied by Grunert, and is subject to qualifications indicated. Grunert warrants for the periods set forth below that products manufactured or supplied by it will be free from defects in workmanship and material, provided such products are installed, operated and maintained in accordance with Grunert's written instruction.


Components comprising a complete system on a new installation are warranted for a period of one (1) year from the date of purchase, but not to exceed two (2) years from the date of manufacture at the Grunert factory.

Grunert will pay labor and travel costs as outlined in its Schedule of Limited Warranty Allowances for removal and re-installation of such components for a period of one (1) year from the date of purchase, but not to exceed two (2) years from the date of manufacture at Grunert factory. OEM installed equipment warranties begin with the purchase date of a new vessel. Costs which exceed the schedule of limited warranty allowances, i.e., parts, labor, limited travel allowance, removal and re-installation time are the responsibility of the customer.

Grunert will repair, or replace at its option, components found to be defective due to faulty materials or workmanship, when such components, examined by an authorized service dealer or a factory service representative, are found to have a defect for which the company is responsible. Replacement components are warranted for the duration of the remaining warranty period in effect on the original component.

This limited warranty is extended in lieu of all other warranties, agreements or obligations, expressed or implied, concerning Grunert components. This limited warranty is extended only to the original purchaser and is not transferable. This limited warranty shall be governed by the laws of the State of Florida and gives the original first end user definite legal rights.

This limited warranty does not cover damages incidental and or consequential to the failure of Grunert equipment including but not limited to; normal wear, accident, misuse, abuse, negligence or improper installation, lack of reasonable and necessary maintenance, alteration, civil disturbance or act of God.

No person or dealer is authorized to extend any other warranties or to assume any other liabilities on Grunert's behalf, unless authorized in writing by an officer of Grunert.


Grunert is a Marine Air Systems company.

Every precaution has been taken in the preparation of this manual to insure its accuracy. However, Marine Air Systems assumes no responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of this product and information contained herein.