Heat loss on a 420 sel
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Newbie
Joined: Feb 2003
Posts: 2
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From: chester NY
1987 420 sel
Heat loss on a 420 sel
HELP
Problem: No heat
Car mercedes 1987 420 SEL
How the problem appears
Start the car with the heat on i.e. the climate control wheel is on red and or MAX. Center console control on EC, or normal, or up and down hot air, heat is fine - WOW I mean hot. Thermostat is fine and new 80C MB original unit. With the car parked the heat will stay on forever. With the car parked rev up to over 20000RPM the heat dies and never comes back on. Restart the car the heat is instantly back. Backup to over 2000 RPM heat dies and stays dead. All this is with the heat control valve on MAX or 26C. Tuen the heat control valve back to white or green the heat turns off as it should. However, turn it back to red the heat does not restart EVER. Turn the engine off and on again heat is back and stays back. Rad flushed out. Whn you drive it the same symtpoms. Drive for 2 hours in the cold heat never comes on. PArk switch engine on and off revs below 2000 heat back on. What the hell is going on?
Problem: No heat
Car mercedes 1987 420 SEL
How the problem appears
Start the car with the heat on i.e. the climate control wheel is on red and or MAX. Center console control on EC, or normal, or up and down hot air, heat is fine - WOW I mean hot. Thermostat is fine and new 80C MB original unit. With the car parked the heat will stay on forever. With the car parked rev up to over 20000RPM the heat dies and never comes back on. Restart the car the heat is instantly back. Backup to over 2000 RPM heat dies and stays dead. All this is with the heat control valve on MAX or 26C. Tuen the heat control valve back to white or green the heat turns off as it should. However, turn it back to red the heat does not restart EVER. Turn the engine off and on again heat is back and stays back. Rad flushed out. Whn you drive it the same symtpoms. Drive for 2 hours in the cold heat never comes on. PArk switch engine on and off revs below 2000 heat back on. What the hell is going on?
Member
Joined: Sep 2002
Posts: 220
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From: Westchester Co. NY
99 C43 AMG & 2008 Corvette 1LT Z51 LS3
Sounds like you need a Heater Valve.
Its pretty easy to check yourself.
Remove the Radiator Cap then Squeeze the upper radiator hose and reinstall the radiator cap while holding the hose. This will creat a vacuum in the system and not allow the coolant to leak out while you check it.
The valve itself is located on the Firewall. You will see a plate about 1.5 inch square with a chrome cap and an electrical connector with 2 pins on it. There are 4 screws that hold it on. Remove the 4 screws, then pick the unit up by the cap. As long as you hold it from the cap, the other pieces attached to it will not come apart.
At the bottom end of it there is a rubber cup. Pull out the end of the plunger about a half inch and Look at the rubber cup and see if there are any cuts in it. If there is a cut in it, that is your problem.
Its a very common problem with those cars!
Its pretty easy to check yourself.
Remove the Radiator Cap then Squeeze the upper radiator hose and reinstall the radiator cap while holding the hose. This will creat a vacuum in the system and not allow the coolant to leak out while you check it.
The valve itself is located on the Firewall. You will see a plate about 1.5 inch square with a chrome cap and an electrical connector with 2 pins on it. There are 4 screws that hold it on. Remove the 4 screws, then pick the unit up by the cap. As long as you hold it from the cap, the other pieces attached to it will not come apart.
At the bottom end of it there is a rubber cup. Pull out the end of the plunger about a half inch and Look at the rubber cup and see if there are any cuts in it. If there is a cut in it, that is your problem.
Its a very common problem with those cars!
