Revised 07/02/2015
"How I Do It"

Replacing the heater control valve in a 300J

by Carl Bilter

The heater control valve in our letter cars controls the rate of coolant flow through the heater core, allowing the heater blower motor to circulate heated air through the passenger compartment. On air conditioned cars, the heater control valve can be closed to prevent coolant flow through the heater core, allowing the air conditioning system to provide the full cooling capacity for which Chrysler was well known.

After 50 odd years, the factory heater control valve has likely failed and has a tendency to leak coolant. As the valve is located inside the passenger compartment, on the firewall just below the windshield on the passenger side, it will leak coolant down the firewall and into the passenger footwell carpeting and pad, and/or onto the passenger floor mat (if so equipped). A leaking valve must either be bypassed or fixed, as it will ruin the carpeting. Replacing the valve is not a fun job on the 300J. In fact, most of us would probably rather be chained to the back of a tank and taken for a scrape with one's head nailed to a coffee table than change the heater control valve. But it can be done with care and lot of patience!

Most if not all of the factory heater valves were supplied by Ranco. On the 300J, the valve is a Ranco H16.

The Ranco valves for our letter cars have not been available for decades. However, there are a number of vendors who will rebuild your factory valve to perform like new. The location of the valve on the 300J is way up above the blower motor. As previously mentioned, it is no small task getting access to the valve. To begin, one must remove the glove box. This is the easy part. I find that removing the glove box door makes the job easier. Next, the glove box light will need to be removed. The bulb and socket will release from the housing by pulling towards the glove box interior. The bulb, socket and wire can then be pulled through the access hole in the glove box. The glove box light housing can be removed by prying it out towards the passenger compartment. Next, the glove box itself is removed through the glove box door opening. After unscrewing the box, flip the box up towards the firewall and remove the left side (towards the console) first and then the right side. This will help minimize damage to the glove box. It is not necessary to remove the passenger seat unless you have a very large girth. Similarly, it is not necessary to remove the blower motor assembly unless you have very large hands, as the space above the blower housing is very tight. Removing the blower housing is a major task itself as it is a one piece unit attached to the vacuum controlled heater doors that are located behind the console. On the 300J, the top bolt for the blower motor housing is blocked by the heater valve when installed; so the housing must be installed before the heater valve is positioned.

The valve can now be accessed. Remove the inlet and outlet heater hoses from the valve under the hood. Remove the cover on the evaporator for the "capillary tube" wire on A/C equipped cars and remove the wire and coil. The valve is held to the firewall with two screws. Remove the screws and push the valve back towards the passenger compartment along with the coil wire (if so equipped).

The valve has a bowden cable attached to it that controls the opening and closing of the valve from the heater control on the dash. Due to the tight fit, the bowden cable cannot be easily disconnected with the valve way up there on top of the blower housing. Therefore, remove the heater control bezel from the dash and disconnect the bowden cable at the heater control lever. The cable is attached with a speed clip. Be careful not to lose the clip!

Now, you can carefully slide the heater control valve along the curved surface of the blower motor towards the passenger side kick panel and insulation. It will slide past the vacuum module attached to the blower housing, at which point you can now finally disconnect the bowden cable at the heater valve by removing the speed clip. If you have made it this far, the valve can now be removed from the vehicle.

I sent my valve to Joe Hudacek in Wisconsin for rebuilding. Joe offers a quality rebuild for a reasonable price (I paid $85 in 2013 and that includes return shipping), and Joe can typically turn the valve around in 24 hours. In addition, the part is returned "all purtied up" as seen in these before and after photos.

The procedure to reinstall the heater control valve is the opposite of removing it. Reinstallation is also more difficult than removal. Be patient! When hooking up your heater hoses to the valve, ensure that the hose routing is correct. If you reverse the connections at the heater valve, you might experience lack of heat at high speeds, water valve rattle, and possibly a damaged or leaking heater core. This diagram illustrates why this will happen. You can see that the valve is designed to flow only in one direction. If the coolant is flowing in the opposite direction it will have a tendency to force the valve seat closed.

I have also discovered that not all Ranco H16 valves are the same. Here is a photo that shows two H16 valves but they have different part numbers. The valve on the right has a thicker capillary tube, the springs in the valve are different and the valve body is reversed. Whether or not the rebuilder reversed the valve body by accident is unknown. But if your car has a valve like this one then your heater hoses do, in fact, need to be reversed so that the heater inlet hose goes to the valve body inlet (the curved section).

Assuming your car has a correct valve, the correct routing for the 413 engines is shown here:

If your letter car has a non-factory replacement heater control valve, such as an EverHot valve, it may not be rebuildable. You will need to source a correct Ranco valve core or your rebuilder may have one available in stock.