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#1
12-06-2003, 08:43 PM
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73 280 heater blower
Hi!
I just found this forum. It looks great. I hope you can help me with my problem . I just replaced the water pump on my daughter's 73 280 (her first car) and now the heater blower doesn't seem to function on heat/defrost settings. It does work with the a/c on however and it worked prior to my replacement of the water pump. Did I do something dumb or am I overlooking something obvious? My only guide is a 75-81 Chiltons import book. Thanks, Ed 
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#2
12-06-2003, 11:59 PM
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The 280 has 2 separate heater and AC fans operated by the same fan switch. There's a vacuum operated change-over switch above the gas pedal, fastened to the left side of the heater box, that switches the circuit from AC fan to heater fan when you turn the AC control fully off, and vice-versa. Look up under the dash above the gas pedal to see if the change-over switch is functioning while you twist the AC control on and off. Check the fuses. If they're OK, while the AC control is fully off, you can use a voltmeter or 12 volt test light to check for power at the fan connector. The connector is located under the hood on the drivers side firewall, near the power-brake booster. If there's power at the connector but no fan operation, a new heater fan is a major job!
Happy Motoring, Mark
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DrDKW
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#3
12-07-2003, 11:51 AM
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Thanks for the info Mark. I've located the switch over the gas pedal. I can activate it by hand and make the fan run. What is the source for the vacuum to trip the switch? I'm thinking that I must have disturbed the line.
Thanks Again! Ed
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#4
12-07-2003, 12:31 PM
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The vacuum source is usually taken off a fitting somwhere on the intake manifold. Some cars also use a vacuum feed off the line to the power brake booster. Not sure exactly where on your 280, as your engine is different than my '72 250. I've also heard that some 280 models used a supplemental engine-driven vacuum pump. Note that any major vacuum leak could affect the operation of the fan change-over switch so check all the vacuum lines and fittings, especially in the vicinity of your water pump repair.
Happy Motoring, Mark
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DrDKW
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#5
12-07-2003, 12:41 PM
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The accessory vacuum runs off the intake in back of the carb. The line goes into a bunch of tees on the firewall, and I think there is a storage tank somwhere. I believe the line to the AC is blue or green. If this doesn't help, let me know and I'll dig out the CD.
The vacuum pump "bridges" the brake booster and a separate fitting on the front of the manifold. Welcome to the Vintage Forum!
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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#6
12-07-2003, 04:58 PM
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I coudn't find any errant vacuum connections but in deference to the 20 + inches of freshly fallen snow in my yard, I opted to duct tape the switch in the appropriate position. I'll fix it correctly when it is a little more temperate.
Thanks again for the advice. Ed Sheehy Franklin MA
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#8
12-08-2003, 10:49 PM
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Aaron,
Oh, I'm sure if I can do one in only two days, you can too. Is it that avocado green one? Happy Motoring, Mark
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DrDKW
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