87 300D heating system problem

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87 300D heating system problem

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Mercedes Forum >> Mercedes Benz Models >> Diesel Discussions >> 87 300D heating system problem

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87 300D heating system problem - 4/18/2007 8:31:41 PM

JamesWendell

Posts: 2
Joined: 9/26/2004
Status: offline

I have had the HVAC dash control replaced last year. Over the winter I ended up with no heat. There was a clicking noise from a valve (?) near the battery. I disconnected the cable at the top and I have plenty of heat. (Too much on a less than cold day.) What is this unit and how does it affect the HVAC system? Is there a good chance that if I replace it my problem will be solved?

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RE: 87 300D heating system problem - 1/5/2009 4:42:36 PM

jimishadow

Posts: 43
Joined: 7/10/2008
Status: offline

monovalve

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79 300sd,84 300sd,85 190d,87 300d,88 300 se,88 190d, 87 300sdl,

(in reply to JamesWendell)

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RE: 87 300D heating system problem - 1/6/2009 4:46:36 AM

ForcedInduction

Posts: 893
Joined: 5/20/2006
From: Federal Heights, Colorado
Status: offline

Monovalve is right. Inside is the valve itself, the housing does not need to be replaced unless the magnetic coil is shorted out.

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1980 240D 3.0VNT 222K Miles. OM617.95, GT2256V VNT turbo, 4-speed manual, 3.46 diff, 15mm rear swaybar, ALDA removed, no EGR and Amsoil by-pass oil filter. Currently 107HP and 195lb/ft of torque at the wheels.

www.youtube.com/Turbo617

(in reply to jimishadow)

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RE: 87 300D heating system problem - 1/7/2009 5:03:02 PM

boblo_home

Posts: 36
Joined: 6/11/2007
Status: online

The Automatic Control System HVAC is faulty by the look of it. I doubt it is the monovalve. The valve is controlled by 12V. Fully open when NO voltage or disconnected, fully close with 12 volt. Anything voltage in between is to control the opening gap for the hot water to flow through.

If you have heat when cable is disconnected then it means it opens OK. The cable is stuck at 12v even when heat is called for. Put the car on full heat, remove the connector and measure the cable connector with a voltmeter. Wait a while for the unit to settle. If it reads 12v ALL the time then the HVAC is faulty. Also your axuiliary pump is OK as you have heat when you removed the connector.

Good luck.

(in reply to ForcedInduction)

Post #: 4