Preface 1

Key Points to the Installation 1

Designing the Refrigeration Box 1

Determining Holdover Plate Size 1


A. Compressor Mounting 2

B. Installation of the Flow Thru Condenser 2

C. Installation of Receiver Assembly & Charging Procedures 3

Start Up & Service 4-5

Manufacturers Limited Warranty Agreement 6


1. ED75 Pallet (G2020007)

2. ED150 Pallet (G2020008)

3. ED75 Holdover Refrigeration System Overview (G2030004)

4. ED150 Holdover Refrigeration System Overview (G2030005)

5. Dual Solenoid Junction Box Wiring Diagram (G8010001)

6. Triple Solenoid Junction Box Wiring Diagram (G8010002)

7. Holdover Plate Sizing (G6030001)

8. Holdover Plates Connected In Series (G6030004)

9. Holdover Plates Connected To Two Circuits (G6030007)


This manual is intended to provide the information necessary for the proper installation and operation of the Grunert 150ED and 75ED engine driven refrigeration systems. Before you proceed, please read this manual completely. Most installation errors and subsequent operation problems are the result of poor attention to the details covered in this manual.


Original Printing: 3/88

Last Revision: 1/98, 3/98


1. Determine the location and type of mounting of the engine driven refrigeration compressor.

2. Determine the size, location, and mounting of the holdover plates.

3. Lay out tubing and wiring before starting.

4. Locate the flow through condenser and receiver assembly before starting.


A well insulated refrigerator or freezer box is the key to an efficient holdover system. We recommend no less than 4 inches of 2 lb. density polyurethane foam (R-55) for the freezer and 2 to 3 inches of 2 lb. density polyurethane foam for the refrigerator. Any more than this would certainly improve the holdover performance of your system. Top loading boxes are always the preferred design. Front loading boxes are very inefficient and should be avoided. A moisture barrier (foil or mylar) should be used around the outside of the insulation.


Determine the 24 hour heat leak into your freezer or refrigerator by using our BTU calculation chart provided. After establishing the 24 hour heat leak into your box, a proper holdover plate size can be determined. If the sum of the BTU capacities of the holdover plates are equivalent to the 24 hours BTU heat leak of the box, a 24 hour holdover time should be realized. Additional holdover plate capacity would reflect additional holdover time. More than 10 percent over capacity on refrigerator plates (26 degrees) is not recommended due to risk of freezing food. All holdover plates are dual circuited so that in the event that a shore side 110V backup is required, the two systems can be used independent of each other to freeze the same holdover plates. If only one system is used on the plates, the two parallel circuits are tied together in series to act as one evaporator coil.



The 75ED and 150ED compressors come with a spring-loaded idler assembly to facilitate mounting either on or adjacent to the engine. This spring-loaded mounting assembly is designed to prevent undesirable shock loads in either direction while also maintaining proper belt tension. It is important that in either case the compressor be securely mounted so that the pulley on the compressor aligns with and is on the same plane as the crank shaft pulley on the engine.

NOTE: The 150ED compressor may be mounted on either side or preferably vertical with the valves at the top. When an idler pulley is used, it must ride the slack not the pulling side of the belts. The idler pulley should be installed in the closest position on the pivot bar for short belt installations. The outboard position should be used for longer belt installations. Adjust the spring just enough to prevent the belt's slip. The 75ED compressor must be mounted so that the refrigeration connections are not in excess of 45 degrees from vertical. Belt should be AX or A type, ½ inch belts. Do not use fractional HP belts. Loads vary from ½ to 3 horsepower.

The 150ED compressor should not be rotated in excess of 1,500 rpm's at the normal cruising rpm's of the boat's engine. The compressor for the 75ED unit should not be rotated in excess of 2,500 rpm's at the normal cruising speed of the engine. Both compressors may be rotated in either direction. Both compressors will tolerate greater speeds, but no decrease in run time will result and the longevity of the compressors will be decreased.

NOTE: To determine the proper engine pulley size (when it is not furnished by Grunert Refrigeration) use the following:

Model 150ED ­ Divide engine cruising rpm's into 10,500 (7 inch clutch times 1,500).

Model 75ED ­ Divide engine cruising rpm's into 13,750 (5.5 inch clutch times 2,500).

Both models use a polyolester refrigeration oil and should maintain a 7 oz. level in the compressor after operation.


The flow thru condenser is connected into the sea water circuit of the engine. It should be mounted as close to vertical as practical. The sea water enters the bottom of the condenser and exits through the top. Use of water fittings of the same size or larger as the existing water supply to the engine are recommended. The ½" refrigeration flare fitting should be connected to the copper tubing coming from the high side of the compressor. The ¼" refrigerant flare fitting should be connected to the ¼" line leading to the receiver assembly.

The ¼" line from the flow thru condenser is connected to the ¼" flare fitting on the suction accumulator, located on the A - HX - R assembly (accumulator, heat exchanger, receiver). This pallet should be mounted in a vertical configuration on a bulkhead adjacent or near the engine. ½" copper tubing should connect to the ½" fitting on the accumulator, to the low side (suction) hose from the compressor. A ¼" copper tube should connect the base valve of the A - HX - R to the expansion valve on the plate (or in the case of a dual box, the solenoid tee). The ½" base valve is connected with ½" tubing to the suction side of the holdover plate (or in the case of a dual box, the check valve tee).


Instructions for turning valves are given clockwise (CW) and counter clockwise (CCW). Close gauge manifold hand valves (CW) before shutting off the vacuum pump. Check to see that both gauges continue to indicate a deep vacuum. If gauges show a pressure increase toward zero pound gauge, a leak is indicated. If this happens, disconnect center manifold gauge from vacuum pump and connect to refrigerant supply. Purge hose by opening (slowly) can or cylinder valve and loosening and retightening hose at manifold. Open both valves on gauge manifold (CCW) and allow refrigerant supply pressure to enter system. Check each connection for leaks with soap solution or leak detector. If a leak is found, repair and recover refrigerant and reattach vacuum pump and re-evacuate for no less than one hour. Once it has been determined that all connection and fittings are leak free, open receiver valves and base valve on the A-HX-R assembly and turn them CCW as far as they will go. Remove the gauge manifold and replace the gauge port caps tightly. The charge will release into the system upon opening the valves.

Reopen the refrigerant supply and purge the air from the hoses. Close the high side gauge manifold hand valve (CW). Open the low side gauge manifold valve 2 turns (CCW). (NOTE: On the 75ED, turn the outer base of the compressor drive 6 turns by hand to clear oil from the cylinders.) Start the engine. Turn on the timer and the thermostat and charge the system with refrigerant. Use proper charging procedures for type of refrigerant being used.

The systems should be charged until the sight glass clears. The expansion valve bulb must be tightly secured on top of the return line of the last plate in the circuit. Clean that section of the tubing making certain that good complete thermal contact is assured. Metal clamps must be used. Take care to assure that no capillary tubing going to the bulb from the expansion valve is in contact with cold tubing or another plate.


The Grunert engine drive units are especially equipped for "pumping out" using a vacuum pump.

The A-HX-R receiver assembly has a receiver valve and a base valve. Both are mounted for isolating the dehydrator and are to remain closed until pump out and leak check steps are completed.

Installation requires a refrigeration gauge manifold with hoses having Schraeder valve depressors. Connect the low side (suction) hose to the low side service port on the compressor and connect the high side (liquid) hose to the high side service port on the compressor.

The hoses are connected to the service ports on the compressor valves. Suction and discharge valves need to be opened one full turn clockwise to energize (150ED).

Instructions for turning valves are given clockwise (CW) and counterclockwise (CCW). Looking down on the valve stem of the valve, turn the valve CW as far as it will go. This will close the normal flow of refrigerant through the valve (valve is front seated). Turning it CCW as far as it will go puts it into normal operation position and closes the gauge port (valve is back seated). When a gauge manifold is to be connected to an operating system, the gauge port cap should be removed only when the valve is back seated.

Connect the center manifold hose (usually yellow) to the vacuum pump. Open the gauge manifold and hand valve, turning them counterclockwise (CCW) and start vacuum pump. On the 150ED models, the compressor discharge and suction valves must be opened by turning them CCW as far as they will go. Without starting engines, turn on 12 volt circuit and set timer to 60 minutes. Set thermostat to four. NOTE: The clutch will disengage when the pressure drops below 7 inches of vacuum, but indicator lights will remain on. Operate vacuum pump until timer shuts off.

Occasionally expansion valves used on Grunert systems will need adjustments after the plates have been frosted and should be adjusted so that suction return line leaving the box frosts no more than 12" from the box. The adjustment is a " square valve stem under the acorn nut on the expansion valve. It should be turned not more than ¼" turn at a time and the system should be allowed to settle out for 15 to 20 minutes before further adjustment. After charging is complete, disconnect the hoses from the compressor service valves.

Turn the suction valve (blue) and the discharge valve (red) counterclockwise as far as they go to close gauge ports and remove gauges.

On both systems, replace gauge port tightly.

The system wiring is a simple series of circuits from the supply panel or batteries, to the timer, to the thermostat, to the pressure switches (receiver assemblies), to the compressor clutch. On dual cabinet systems, the thermostat controls the solenoid valve in the liquid line to the refrigerator expansion valve.

NOTE: Potted low pressure switches have a 7 inch vacuum cut out and 10 lb. cut in.

INSTALL ELECTRICAL WIRING AS SHOWN ON THE WIRING DIAGRAM. A larger, never smaller, wire may be used if wire sizes are not available. NOTE: Wire size decreases with larger numbers.

IMPORTANT NOTE: All units must be grounded using an independent ground wire. A minimum number 12 wire should be run from the A - HX - R to a bolt on the engine or grounding terminal. On metal boats where a completely ungrounded system is run, an isolated or floating ground should be used for the 75ED, the compressor should be on an isolated ground from the engine on metal hulled boats. The holdover plates are usually secured using stainless steel self-tapping screws or expanding type blind fasteners.

The thermostatic switch (T-stat) operates on plate temperature. The last four inches of its capillary tubing should be inserted into the ¼" tube provided for it on the last plate ­ that plate furthest from the expansion valve. As with the expansion valve capillary, no part of the thermostat capillary, other than the last four inches, should be in contact with any cold lines or plate surfaces. Thermostatic switches are furnished with long capillary tubes so that the switch may be located outside the refrigerated area. This is the preferred location. Do not run the refrigerator T-stat capillary through a freezer compartment.

Refrigeration flares must be perfect, as faulty flare connections are prone to leaking. Check your flaring tool. If the cone is scratched or damaged, do not attempt to make refrigeration quality flares with it. The purchase of an Imperial 500 - FARL-AIR flaring tool and its use exclusively for the refrigeration connections is recommended. An occasional drop of oil on the flaring cone assists in making good flares.

Be certain that flares are expanded to provide a complete seat on the fittings. Do not over flare. If the flare is overexpanded and touching the flare nut threads, do not attempt to draw it up. Remake the flare. The flare should almost fill the flare nut but not touch the threads.

Where flare connections are subject to frosting such as those between evaporator plates and all suction line connections, a compound such as LeakLock® or other un-hardening compounds should be sparingly used on the male threads to prevent frost and ice from forming in the threads and loosening the nuts. Great care must be used to prevent any compound from getting on the flare seat. Hold the male fitting with a wrench and turn only the flare nut while tightening a refrigeration connection. ¼" tubing connections must be pulled tight but not pulled up so hard that the flare seat is crushed. ½" flares must be pulled up as tightly as you can and leave enough slack in the tubings so that the connections may be cut off and remade if necessary.


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. Warranty will be paid in accordance with our established schedule of allowances.

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, Inc. 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.