Packard Forum Index » V-8 (1955-56)

It is a pleasure to see the quality and pride that went into items manufactured in years gone by so the stainless valve set on a swiveling ball seat on the brass plunger providing an almost air tight seal should not come as a surprise but in probably one of the least expensive parts used on the Packard except for hardware it still is amazing . The stamping of the script logo and columbus with united states of america written out and not abreviated was interesting as the lettering alone probably cost more than some of the plastic parts used on todays supercars. I was wondering why the capilRy tube and bulb is not run into the heater box as in other manufacturers applications? Did Packard miss the mark here? It seems this eliminates the automatic compensation feature of the unit causing it to be just a manually controlled on or off. I read through the info on the refirb and a mention of ensuring to not damage the tube is made but in this case elimination of the tube and the tiny screw at the dashpot tip would give manual function. I assume the capiilary tube bulb would need to see the temp differential between 40 and 150 degrees as the other applications or did Packard have a different spec for the bulbs used? Seems unlikly. Strange the unit is sensing just the interior temp of the vehicle or more so the firewall temp.

Apparently Packard found that inside the box didn't work well with the thermostats they were using. When they introduced the thermostatic valve in 48 the bulb was inside the plenum sensing nothing but the heated air. Shortly after the 22nd series intro they said that location was not satisfactory and had dealers remove the bulb from the heater box and place it under the glovebox so it could sense ambient air (Dec 1, 1947 Service Counselor). They specifically told the mechanic to make sure free air could circulate around the bulb. In the units from 24th series on they used a different valve. It was placed next to an opening in the plenum and heated air was directed to blow past the sensing element. I guess they figured that was the best way with that valve so it could sense both ambient air and also monitor that the heated air was not too hot

LIke a home thermostat if you put it under the a vent, it only "reads" the temp coming out of the vent, as opposed to the ambient temp in the room, or in this case the cabin. So it could keep shutting of the heat prematurely as the vent heat would be very hot compared to the temp in the cabin.

Thanks. I did not realize there was a service counceler relating to this. I will have to make a habit of searching these even for earlier model years. Perhaps it was Packards intent to eliminate the automatic function for a manual system. As I recall the capillary tube and bulb tip work in conjunction to sense the difference between the ambient and delivered air. The plunger tip has very little movement at temp differentials of 30 deg to 90 deg(less then a 1/16).It will have a quarter inch or so if the bulb is in 150 and the coil tube is at 75-80. Seems unlikely the unit could have any automatic function installed in this application.
The bulb in the plenum chamber also will allow the unit to compensate for extreme differences in the outside air temp and the htr cores ability to heat air of 20 deg as opposed to 55 deg.