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560 SL Cabin Temperature Sensor Hose Repair

A Step-by-Step Tutorial by GlueckAuf

As part of a sophisticated, well-engineered automatic climate control system, the 560 SL’s dash-top

cabin temperature sensor was apparently designed to gently draw cabin air into it by way of a rubber

and foam air hose underneath the dash that employs a mild vacuum from the heater box. While the

rubber hose should last indefinitely, the foam hose tends to deteriorate after some number of years

(mine lasted 23). Eventually the hose assembly’s 7” foam section falls to pieces and the cabin air drawn

into the sensor is all but lost. As a consequence, now-stagnant air at the temperature sensor prevents it

from sensing rapid changes in cabin air temperature. On a hot, partly-cloudy day, for example, the air

conditioner system’s thermostat seems to cause the AC compressor to run a little too long on its cooling

phase, and then allows it to remain off a bit too long on its coasting phase. Thus, the cabin temperature

cycles between frosty cold and humid warm (assuming the AC is otherwise up to snuff.)

So what’s with the 7” foam section, anyway? Why didn’t Mercedes just use a solid rubber hose for the

entire length? I can only surmise that the foam piece is there to either further reduce the volume of air

drawn past the sensor, or to provide relief if the air slots of the sensor were to become blocked by

objects placed on the dash.

The entire hose assembly, Mercedes part number 107.830.07.96, and described on the Electronic Parts

Catalog as“Hose Between Temperature Sensor and Air Nozzle”, is available from your local dealer or

from any number of online sources for about $30 to $40. But if only the foam section is worn out, you

can replace it for less than $2.00, and this simple guide will show you one way how.

To perform this job you’ll need the following new parts and tools:

1. A 7-inch (18 cm) piece of ½” (1.3 cm) Inside Diameter Insulating Foam Hose, about $1.60 for a

six-foot length from Lowes. (This type of foam hose is used for insulating residential air

conditioner refrigerant lines, and is only (?) available in a split, self-adhesive variety.

2. Scissors

3. Double-Sided Acetate Tape

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Figure 1. Here's the thoroughly deteriorated, twenty-three year old original foam section of the cabin air temperature sensor hose. When this piece fails, one consequence is poor thermostatic regulation of the air conditioner.

Figure 2. View from inside the glove box opening looking left. Before it fell apart, the foam section of the cabin air temperature sensor hose ran between the removable rubber fitting on the barbed temp sensor at the top of the picture and the rubber hose at the right. The rubber boot for the dashboard center air outlets is beneath the white nylon temperature sensor.

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Figure 3. Begin the job by removing the glove box. The first step is to remove the glove box light. A clip on the end facing you holds it in; lower it, pull it free from its hole, then disconnect the two spade electrical connectors.

Figure 4. The glove box is held in its frame by four plugs, two upper and two lower. Each plug is secured by an expanding pin. With a fingernail or slender blade, gently pry out each fastener’s expander pin and then pull or carefully pry out the expanding plug. When all four plugs are removed, carefully tilt the top of the glove box toward you, lift the lower lip over the door hinges, and then pull the box out and set it safely aside.

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Figure 5. In this diagram taken from the Mercedes-Benz Electronic Parts Catalog, part number 199's upper foam section is the only part that failed. There's no need to replace the whole part when we can graft on an inexpensive piece of replacement foam hose.

Figure 6. If you can find unsplit hose, use it. The only type of 1/2" foam hose at my local hardware store was split, with self-adhesive edges.

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Figure 7. Cut an approximately 7-1/2" section of foam hose. If you're using split hose, join the self-adhesive edges and press them firmly together. For a little extra security, I sewed up the seam with some stout thread. We’ll use Scotch double-sided tape to secure the foam hose to its rubber hoses.

Figure 8. Apply a strip of double-sided tape to the removed temperature sensor fitting, and then insert one end of the foam hose. Press the hose into firm contact with the tape.

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Figure 9. Wrap the end of the lower hose with a strip of double sided tape, slip the hose over the taped end, and press the foam hose firmly into contact with the taped rubber hose.

Figure 10. Plug the upper fitting into the barbed end of the cabin temperature sensor. Check that the center vent boot is still in place, pulling it back onto the nozzle ends if needed.

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Figure 11. To finish the job, route the glove box light cables into the lamp hole in the top of the box and slip the glove box back into its aperture. Reconnect the lamp’s two electrical cables, snap the lamp back into place, and then secure the glove box to its frame with the four plugs and expanders. Switch on the ignition and ensure the glove box lamp and switch work properly.

That’s it! Replacing the deteriorated hose should restore the timely, accurate function of the cabin

temperature sensor. This will improve both the temperature-regulating performance of your SL’s air

conditioning system and the hot-weather comfort of you and your passenger.

Good road,

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GlueckAuf Sterling Heights, MI 1987 Mercedes-Benz 560SL Benzedrine

2002 Volvo S80 T6

2004 Litespeed Vortex/Campagnolo Record