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76 450SEL - Heater problem
The climate control system is working well, but I am getting cold air instead of warm air -- with the heat dial turned all the way to the red zone. What would be the correction for this situation? Must be something in the controls area that is not registering the heater setting ?? What do you vintage experts suggest ??
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Ben Harrison Carter 1999 Mercedes ML320 87K 1992 Mercedes 300CE 89K 1995 Corvette 29K -- Sold Dec 09 1989 Mercedes 420SEL 99K -- (Sold 4/08) 1968 Mercedes 230S (106K) (Sold 9/06)) 1976 Mercedes 450SEL 130K (Just sold - 06) 1961 Mercedes 220Sb (sold years ago) |
#2
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servo check
IF
the 450's servo is the same type as my early 123 280CE (ACCII, a.k.a. Chrysler's Revenge, vertical buttons on control), [If not, ignore my prattling below and proceed directly to next post...] have hood open and be near servo with engine running as someone else turns off engine - you should be able to hear it running for a few seconds as it returns to "park" - at which position, by the way, it should be "failed" to the posit mentioned by Col Klink - at which you should still get warm water, and blowers/doors controls should be bypassed/routed to give you the DEF as an emergency fallback with high blower, up through def vents, and hot water. Manual on the mother-type system at http://imperialclub.com/Repair/Lit/Master/281/cover.htm and procedural checkout at http://skinnerbox.steaky.org/Service/W123/Main.html try under M110, then "78 280CE" (the one I use) under "climate control" - step through to checkout procedure without factory test unit. If followed in sequence, may help isolate area of concern. And of course, there's the Unwired Tools solution at top of Forum page... And some servo rebuilders out there... |
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Well, its NOT working well apparently. Could be a bad servo, bad amplifier, or another component in the chain. There is a temp sensor, the controls on the dash, and vacuum pots to control the flappers. Try the fuse first. Its probably a bad servo, they last only a few years, usually take out the amp when they go.
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#4
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inline fuse
Concur with checking out the amp's wierd little inline fuse up in the relay box - and my MB dealer still had them when I was fixing my daughter's - meter through to check continuity, since not visible strip or glass. Also other fuses to the blower and vacuum relays, as listed in your manual for the 450 (many models use different fuses for this...)
Dunno how your in-car temp sensor aspirates air, in the 450, but my early 280CE uses a tube going to intake side of blower to suck air past a sensor in the RH speaker grille (later versions put sensor in middle of dash) - and that tube had disintegrated to dust...thereby only accidentally getting a sample of the cool air in the compartment temp which then tells it to open the water valve to hot; but that tube should not be a "sudden" failure item...and the resistor values of the ambient air sensor, in-car sensor, and selector wheel shouldn't be so far off as to cause cold vs warm air... The website procedures I cited earlier are really thorough - and also include vacuum checks you can do through the servo's tubing connections without disassembling the whole dash... One quickie, if you're only getting blower in "DEF", is to dummy across the two "T" connectors fed by the two tubes going down to the bottom of your servo - they go to a "warm water sensor" which won't allow blower to operate if it doesn't sense available warm water (thereby preventing cold air from being blown around your sensitive little toes...) |
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450 heat
Thanks for all the good advice; I will be going over the car with a fine tooth comb this week to try pinpointing the problem. Otherwise, I will connect the water hoses directly to the heater core ... so heat is definitely available for the new owner who is picking the car up Tuesday and driving it to Seattle ...
Like all other car problems, I am sure this one is solvable, but just has to be specifically diagnosed... Ben Carter
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Ben Harrison Carter 1999 Mercedes ML320 87K 1992 Mercedes 300CE 89K 1995 Corvette 29K -- Sold Dec 09 1989 Mercedes 420SEL 99K -- (Sold 4/08) 1968 Mercedes 230S (106K) (Sold 9/06)) 1976 Mercedes 450SEL 130K (Just sold - 06) 1961 Mercedes 220Sb (sold years ago) |
#6
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My guess is connecting the hoses directly will not give you heat because the servo/amp control the flappers which control the air flow. You would get hot water in the core, but may not get air blowing over it.
If it is kaput and you are selling the car, I would give the buyer a discount and tell him to get one of the digital replacement units. Kinda pricey (around $700 I think) but its a one time deal.
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#7
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Flappers
No, I am getting flapper control from the dash buttons, so anything that is available in the A/C system or heating core would be available for flow into the car .... everything is working well except the hot water flow to the core.
The new owner may use a ball valve to bypass the servo for the time being and find out the problem with hot water release later, at his leisure -- if I don't find it this week before the car is picked up. I still think the servo itself is OK, but some electrical or vac connection is not. Thanks for all the help guys ..... will let you know the final result.... the new owner is a forum member so he knows exactly what is going on with this system, both from my posts here and in direct email discussion etc. Ben Carter
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Ben Harrison Carter 1999 Mercedes ML320 87K 1992 Mercedes 300CE 89K 1995 Corvette 29K -- Sold Dec 09 1989 Mercedes 420SEL 99K -- (Sold 4/08) 1968 Mercedes 230S (106K) (Sold 9/06)) 1976 Mercedes 450SEL 130K (Just sold - 06) 1961 Mercedes 220Sb (sold years ago) |
#8
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Quick Fix
Try pulling out the electric plugs -3 to the servo then turn your defrost on. If you want an address of a rebuilder -who knows what he is doing -uses an aluminum body -ask. Actually these servos were ok and top of the line for their time, but most people did not flush their radiator every two years to get the small particles out - result stuck, then broken internal valve in the servo. George Murphy wrote a great article for The Star magazine on the care and fix for the servo. He is also the guy that rebuilds them now. E-mail at perfanalysis@comcast.net or georgemurphy@compuserve.com. I can send you the articles via email, just ask.
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#9
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CC Servo
Thanks for the info; I am sure that is one alternative, but still think the servo itself is OK .... will require further investigation of that elaborate CC system to determine the exact cause. There are so many elements of the system to look at, including vac and electrical, that any one of them could be the problem. Ben Carter
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Ben Harrison Carter 1999 Mercedes ML320 87K 1992 Mercedes 300CE 89K 1995 Corvette 29K -- Sold Dec 09 1989 Mercedes 420SEL 99K -- (Sold 4/08) 1968 Mercedes 230S (106K) (Sold 9/06)) 1976 Mercedes 450SEL 130K (Just sold - 06) 1961 Mercedes 220Sb (sold years ago) |
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