Help: 73 280SE 4.5 A/C wont turn on // speedo died - Mercedes-Benz Forum

 
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post #1 of 6 (permalink) Old 11-13-2006, 06:29 PM Thread Starter
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Date registered: Sep 2006
Vehicle: '82 300D turbodiesel, China Blue/Blue, 146k, CLKs & Bilstein HDs
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Help: 73 280SE 4.5 A/C wont turn on // speedo died

Hello all-

I just bought a beautiful white/red '73 280SE 4.5 from the original owner (42K miles).

When I looked at the car 2 weeks ago, the A/C blew cold and the little green light was on between the switches on the unit. On my 150+ mile drive home, the green light wont come on, and I am getting no A/C. All other controls seem to be working.....if they are controlled by the "upper" controls on the dash. It is just the 2 A/C knobs and controls that now seem to do nothing.

I checked fuses under the dash and all are in good shape. I am hoping there is another fuse or relay or something that I should be checking! Can anyone please direct me in the right direction?

Second problem.... on my way home at 75+mph my speedometer suddenly stopped working. Should I investigate the guage itself first, or would a cable snap first? Figure this car drove around a beach community for 33 years and never saw 75mph before. Now it lives in a new beach community and wont ever have to endure that punishment again!

Thank you all in advance for your help..... I searched these topics but didnt have any luck!

Bill

Here's the car I bought if you would like to see..... I paid MUCH less than that asking price ;-)

www.autabuy.com/Vehicles/Details.cfm?VID=70272
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post #2 of 6 (permalink) Old 11-14-2006, 04:02 PM
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Vehicle: 1971 W108 280SE & 1967 W111 250SE Coupe
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Congrats on the new car. On both my 250C and my 1972 280 4.5 the speedo cable was the culprit. They usually get noisy just before they give out. I'm on my 4th vintage MB and never had to replace an original VDO speedo. That's my experience anyway and certainly not gospel.

I think the AC is pretty much a stand alone system, not involved with the other (4) heating & ventilation controls on the dash which are heater blower, floor/defrost, temp right & temp left.

For the OEM under dash AC you have the control to turn it on and engage the compressor (green light) and a speed selector for the separate blower fan inside at the passenger’s side kick panel, if memory serves. That’s about it I think control wise. Seems odd to lose everything, fan & compressor. I'd revisit the fuses, especially the aux / accessory fuses outside of the main panel. They are the little square brown boxes, behind the battery on the firewall with the relays, which also may be suspect.

Last edited by Shab; 11-14-2006 at 04:30 PM.
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post #3 of 6 (permalink) Old 11-16-2006, 02:23 PM Thread Starter
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Shab thanks for the reply.

I have checked all the fuses under the dash, all the fuses on the firewall, and all the relays are clicking properly when I remove them and test them with a battery.

This has to be a wiring issue somewhere..... my A/C unit is completely inop, the green light wont come on, the blower is not blowing, and the fan in front of my radiator doesnt come on either. I assume that should come on when the A/C comes on.

I guess it has to go to the shop for a check-up.
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post #4 of 6 (permalink) Old 11-16-2006, 03:21 PM
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The aux electric fan comes on when a coolant temperature milestone is reached, not simply when you use the AC. It's an aux fan for sitting in traffic, long idling on hot days and such. I forget what the temp has to reach to kick it on.

Hopefully, one of the more knowledgeable members can suggest what the AC issue is. Perhaps something is up with the under dash unit itself since you have lost everything.
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post #5 of 6 (permalink) Old 11-16-2006, 08:13 PM
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i know my 300CE a/c compressor wouldn't come on because of a freon leak. when the pressure switch on the a/c lines on it detected a loss of pressure due to a leak, it cut power to the clutch on the a/c compressor, to keep it from running without any fluid, which also lubricates it.
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post #6 of 6 (permalink) Old 11-17-2006, 07:33 PM Thread Starter
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Thanks to both of you for your help. I am unable to determine the cause of this, so I will take it to a professional next week some time. I lik eto do my own service, but this is beyond my level of understanding!

I have a garage that services my Boxster that I like. They always have a nice selection of old MB's around, so they must know them well.

Thanks again

-Bill
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