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Old 04-16-2004, 08:34 PM
Registered User
Join Date: Apr 2004
Location: Atlanta, Georgia, USA
Posts: 61
1986 300E Climate Control

We've had our 1986 300E for 15 years. It is in excellent condition, but the climate control has frequently been a problem.

This time, the heat is on full; blowers on top speed when in 'auto' no matter where the temperature setting is.

Here's the info from my check-out:
1. The aux water pump works but draws 2.45 amps.
2. The voltage (open-circuit) output to the mono valve is 5.5 VDC.
3. The mono valve resistance is 14.5 ohms.
4. If I disconnect the mono valve and jump 12 VDC to it, cool (not cold) air comes through.
5. I see some air bubbles in the refrigerant sight glass.

I'd like another opinion on my diagnosis:
1. Replace the original aux water pump
2. The original mono valve is okay (should I replace it?)
3. The ACC panel (5 year old rebuild) is bad and should be replaced.
4. I may have a freon leak to fix.

Any comments are welcome. Thanks!

Brent Smith
Atlanta, GA

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Old 04-16-2004, 10:38 PM
Registered User
Join Date: Jul 2002
Posts: 1,141
I think 0.8 Amps is max for the aux water pump. Disconnect it or replace it.
The mono valve is probably fine. I would replace anything that isn't bad, without condemming diagnostics. That gets expensive. You might need freon, but your symptom deals with the Automatic Climate control system.

Have you tested the KLIMA relay yet???

My system is working well and my CD has not come in yet. Hence, I'll leave it to the experts.

I was going to add a 1.0 amp fuse to my aux water pump just as a fail-safe method not to damage the climate control panel. Does anybody else do this or am I wasting my time???

Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E
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Old 04-16-2004, 11:01 PM
pesuazo's Avatar
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Join Date: Oct 2002
Location: Near Raleigh, NC
Posts: 580
I disconnected my Aux. water pump a while back, with no adverse effects.
Its function is well documented, and now that the summer is coming I won't miss it. (Not that I missed it in the winter either).
1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
609 Certified
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Old 04-18-2004, 11:32 AM
Registered User
Join Date: Apr 2004
Location: Atlanta, Georgia, USA
Posts: 61
Confirmed problem--but not fixed

I disconnected the auxilliary pump and then hot-wired the mono valve so that it is closed when the ignition switch is on (bypassing the controller). The controller now works fine operating the blower speed and A/C clutch.

Apparently the controller output to the aux pump and mono valve is fried from the high pump amps (2.45A).

Next step is to replace the controller and re-connect the mono valve (leaving the aux pump disconnected).

Later on, I'll flush the cooling system and replace the aux pump. I think the idea of an in-line fuse for the pump is a good one. I'll probably do that.

Does anyone out there see any problems with my approach?

Thanks in advance.

Brent Smith
Atlanta, GA

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