I smelled ammonia in my 1990 refrigerator.  Well, it did last for 17 years!  But I really didn't want to spend $1300 plus tax and installation for a new one.  I checked out Howell's RV in Santee, CA, at Rick's suggestion.  They wanted about $525 for a refurbished cooling unit.  Next, I went to eBay and found RV Repair.  Their RM 3604 unit was $485 plus $25 shipping with a $100 rebate upon return of my old unit, for a net total of $410.  I clicked the Buy It Now button and the rest is history.

Here's the sales pitch that appealed to me:

By talking to the actual supplier, I found out that what makes the units fail is moisture that gets behind the aluminum fins inside the box and rusts through the cooling pipes.  Also, both Norcold and Dometic now use thinner pipes in the new models, so they don't last as long as the older refrigerators.  Besides the cost savings, that is another advantage of being a do-it-yourself-er!  By the way, the wholesale-only supplier contact information is at the bottom of the installation instructions.

They were helpful in answering my technical questions, as was David Force of RV Repair, by e-mail.  David e-mailed the instructions to me before the unit had arrived, so I could have the old one out and ready to ship back immediately for the rebate.  I had the rebate before I had finished re-installing the refrigerator.  It all went very smoothly.

The two pictures below show, front and back, the shipping box I received via FedEx with the new cooling unit beside it.  I had already put the old unit in the box for shipping back.  Notice the pipes sticking out.  They protrude into the freezer compartment.  Also, note the flat pipe going from one side to the other and back.  That is the contact point for the aluminum fins that go into the refrigerator compartment.  That pipe is what normally rusts through, thus allowing ammonia to get inside the box.

The next picture (left) shows the refrigerator box with the original cooling unit removed.  The slot at the top is where the cooling tubes go into the freezer.  The bigger opening is where the aluminum cooling fins go into the refrigerator compartment.  To the right is the box with the new cooling unit inserted and attached to the back of the box, ready to put back in the Aero Cruiser.

While I was at it, I thought I should add a fan to help cool the heat-dissipation fins at the back when I am in very hot weather.  I added a switch on the control panel at the top of the refrigerator inside the RV.  The switch is powered through a light wire pair from the bottom where I hooked it to the main ground and 12v wires going into the refrigerator electronics box.  You can see the switch on the control panel on top of the box (loose, upside down, and facing backwards in the picture).  You can see the fan mounted below the fins at the top back.  It is a standard "muffin" cooling fan for a computer or other electronics: $5 on eBay.  Above is a close up of the fan and the cooling fins.

Before putting the refrigerator back in, I decided to give it some help by insulating the cabinet it goes into. (Why didn’t they do that when they built the Aero Cruiser?) The interior of the cabinet has some irregularities due to a board brace for the light over the couch and due to wiring. So, I used ½ inch insulation slabs, cut to fit. Then I added another layer, cut differently, as needed. Then I added a third layer for a total of 1½ inches of insulation on each side. I also put five layers over the top for 2½ inches there. Shown below is part of the first layer of insulation, just to give you the idea.

Finally, just before sliding the box back into the cabinet, I mounted an indoor-outdoor thermometer next to the refrigerator and ran the outdoor probe through a hole I drilled in the frame at the hinging edge of the refrigerator- compartment door. The probe line has to go between the door seal and the main box, so it makes a slight breach in the seal, but it is small enough not to create a significant leak. I put enough line inside the box that I can also run it up to check the temperature in the freezer compartment if I want. The picture to the right shows the thermometer, its line that goes inside the box, and the fan switch on the control panel that I added to activate the fan on the back. Of course, the thermometer tells me room temperature and the temperature inside the refrigerator.

Now, I skipped over the technical part: the removal of the old cooling unit from the box and the re-installation of the new unit. That process is described in a set of instructions provided by the seller of the new units. With permission from the supplier, I have edited those instructions to specialize them to the Aero Cruiser’s RM 3604. Mostly that meant deleting some irrelevancies that relate to other models. The simplified instructions are presented below.

If your refrigerator internals, burner, heating elements, and electronics are in good shape, and if you like to save money and get a superior product, you may want to do it yourself. This should let you know what is involved.

Next, remove the refrigerator doors. After that, remove four to six mounting screws on the face of the refrigerator, possibly covered with plastic plugs. See graphic. Look for any other fasteners that might prevent removal of the refrigerator. The RM 3604 has two mounting screws behind the plastic control strip at the top, covered by plugs; either remove the plugs to access the screws or (better) loosen the whole plastic molding by removing two small screws from its underneath.

Next, inside the RV, underneath the refrigerator, there may be a bead of silicone that needs to be cut with a razor knife. The refrigerator should then be free to slide into the RV. If it doesn't move, look around for something else holding the refrigerator in. Sometimes RV manufacturers create their own ways of securing the refrigerator. If possible, take the refrigerator out of the RV to a larger work area.

Removing the Cooling Unit  
Begin by removing the aluminum freezer plate from the freezer. This is held in by four bolts and nuts, with plastic protectors on the bottom side. Remove the fasteners and pull off the freezer plate. This will expose pipes from the cooling unit protruding into the freezer. In the lower box, on the aluminum fins, there is a capillary tube from thermostat held in place by a small plate. The capillary tube is the sensor from a thermostat and resembles a wire. Loosen the plate and remove the capillary from the fins. The fins will stay with the cooling unit until it is removed.

Once the work inside the refrigerator is done, lay an old blanket or cardboard down to protect the refrigerator, then lay the refrigerator down on its face. What we're after is the cooling unit.  It's the set of coils on the back of the refrigerator, extending from the top to the bottom.  Obvious parts such as the electronics box, burner assembly, heat elements, insulation pack, etc., must be removed from the unit.  Anything else in the way of pulling the cooling unit must also be removed.

Be sure to keep track of which screws are removed from where.  Replacing a short screw with a longer screw can harm an underlying component.  The way I usually do that (and did) is to put them right back in the holes until I am ready to put them back in permanently.

There is a handful of obvious screws  holding the cooling unit to the refrigerator that must be removed. See graphic (ignore the “thermostat tube”, as the RM 3604 does not have it, nor does it have the “hidden screws”).

Once all fasteners have been removed, the cooling unit is ready to pull. A pry bar under the "big tube", as in the graphic, will usually do the job. The "big tube" is the only pipe that you should pry on. Since you will be prying against the refrigerator body, a board or some other protection is necessary between the pry bar and the refrigerator to prevent poking a hole in the box.

This is usually enough to pull a cooling unit, but not always. If yours is stubborn, peel up the edges of the aluminum backing paper to expose a line between the foam of the cooling-unit head and the insulating foam of the refrigerator box. If the cooling unit has already been replaced before, the backing may be a piece of sheetmetal instead of paper. With some effort, the sheetmetal can be removed and slid out from the cooling unit. Running a large knife around the line between the two foams of the cooling unit and box (about 4" deep) and then prying as before will remove the more difficult units. If you're still having problems, go back and be sure you have removed all fasteners.

Once the cooling unit is out, remove the three screws from the aluminum fins and pry them off the cooling-unit head. Pull the baffle from the cooling unit chimney and remove any other parts (including the insulation pack) from the unit. These parts will be transferred to the replacement cooling unit. Not transferring the baffle from the old unit to the new one is the most common mistake made by installers. The baffle is a twisted metal strip hanging down the chimney on a stiff wire.

You're now done with the removal.

Note: there is usually a clear plastic sheeting between the foam of the cooling-unit head and the foam of the box. This was there to keep the two foams separated when the foam of the cooling unit was poured while the cooling unit was already in place. This plastic can be discarded if it is torn or in bad shape. This is also why there can be a little difference between the foam heads of cooling units.

Installation  
Inspect the rebuilt unit that you are going to install for freight damage. One common problem that is easier to fix before installation rather than after is a bent freezer coil. The freezer coil should be perpendicular to the back of the cooling unit. If the coil is bent, you can use a bar, as in the graphic below, to level the freezer coil.

The key to a successful cooling-unit installation is a snug fit between the cooling-unit head (foam block) and the box, with the head all the way into the cavity of the refrigerator and no air leaks. By all the way into the cavity, we're referring to the face of the foam block. Sometimes, because of refrigerator variations, the head is thicker than the cavity and protrudes a little out the back. This is OK, as long as the front of the head is flush with the inside of the refrigerator. The part sticking out will be taken care of later.

In the graphics below, the is a metal to metal contact point that requires thermal mastic. The refers to a fit point -- a point where the cooling unit has to make good, snug contact with the refrigerator box.

The first step in installing a cooling unit is to apply thermal mastic to the coils of the cooling unit that contact the aluminum fins of the refrigerator. Before doing that, be sure the cooling unit pipes are making contact with the fins, without the foam of the head preventing that contact. Sometimes the foam needs to be grated down to allow this contact. See graphic.

After the mastic has been applied, secure the aluminum fins to the cooling unit. Be sure to well tighten the screws that mount the fins and replace the plumber’s putty around the baseplate so it will seal against the inside back of the box. There are brackets for the screws below the surface of the foam. On our rebuilt units the holes in these brackets are drilled a size too small, so that your screws will get a good bite. You should see the screws slightly pull the area around them inward. Getting the fins on tight with mastic is critical. Failure to do so will cause cooling problems in the lower box. (Later you will also put mastic on the freezer coils, before installing the freezer plate.)

Next, before sealing the edges of the foam block of the cooling unit and permanently installing it into the refrigerator, it's a good idea to place the cooling unit into the refrigerator to see how well it fits. Sometimes the foam block is too big and needs to be trimmed. Don't get carried away with trimming. A rasp works well. Often, after a test fit, you can see marks on the side of the foam that indicate a high spot. Once comfortable with the fit of the cooling unit, put about a half inch bead of "Silicone or Latex Caulk" around the back edge of the foam block (on the inside face of the aluminized backing sheet) and place the cooling unit into the refrigerator. See graphic.

Next, install the mounting screws for the cooling unit. It is important that the two top mounting screws line up with their corresponding holes in the refrigerator. Although all the mounting holes of the cooling unit should line up with the refrigerator, the top two are the most important because they set the angle of the condenser. Also, it is not unusual for this part of the cooling unit to get bent in shipping. If the cooling unit is bent in such a way, it can usually be straightened by running a pry bar through the top pipe of the cooling unit’s big tube and over the edge of the refrigerator box and prying upward. Failure to get the top two screws in their respective holes may cause the cooling unit not to work.

Fasten the lower half of the cooling unit to the refrigerator in such a way that the boiler (the pipe inside the insulation pack) is parallel to the side of the refrigerator. Normally lining up the cooling-unit holes with the holes of the refrigerator accomplishes this. But if it doesn't, it is permissible to move the lower half of the cooling unit (after the top half has been secured) so that the boiler is parallel to the edge of the refrigerator and start new mounting holes. Before the cooling-unit body is fastened down, use aluminum foil tape to secure the thin backing of the cooling unit in such a way that it is virtually impossible for air to get into the refrigerator from the back. If the head (foam block) protrudes above the surface of the refrigerator box, this is the time to take care of it. A good tape job along the edges will suffice. Now install, align, and tighten the screws that fasten down the cooling-unit frame.

Install all the peripherals that you had removed earlier (heat elements, baffle, burners, insulation pack, etc.). The mounting bracket on the cooling unit for the burner is like the one in the graphic.  It is important that you use the original machine screws that were removed from these holes when replacing the burner. Using other screws may actually "drill" a hole into the cooling unit, discharging the coolant. In other words, it will make a dangerous, nasty mess and ruin the cooling unit.

Once everything on the back of the cooling unit has been installed, set the refrigerator upright. Put mastic on the freezer coils in the freezer and install the freezer plate. Reinstall the thermostat capillary tube to the fins in the lower box.

Installing the Refrigerator  
Install the refrigerator back into the RV and make the necessary connections for the electrical and gas. Test for propane leaks at the connections you have made and all gas parts on the refrigerator. The refrigerator should set upright about 30 minutes before being put into operation. If possible, test the refrigerator on 120 volt first, only because there are fewer variables on the electrical side than on propane. You should see signs of cooling in the freezer in 1 to 1½ hours, and an empty box should come down to temperature in six to eight hours.

Thanks to: 
Pines RV Refrigeration
(Larry & Lisa Miller)
5930 W 200N
Shipshewana, IN 46565
Web site Store on eBay
260-768-7990
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