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'88 500SEC HV, '84 7MA61 Supra, '83 JZA61 Supra
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369 Posts
Discussion Starter #1
Hi all

After not having any heat from the heater and a running temp of about 65degrees Celcius, I replaced my thermostat- now have the correct 80-85 deg C operating temperature.

However, I still have no heat.

My car is a euro 500SEC with a duovalve and dual wheel setup. No heated seats etc.

I have checked the voltages of the rotary switches and they work correctly, sending +12v to the duovalve.

I have also put +12v on the duovalve and both valves open and close (well, they click).

The plot thickens however, when sometimes I start the car:

- I have heat on the passenger side but not driver’s side.
- The recirculation light is on as soon as I start the car- I haven’t pushed it.
- The auxillary (A/C) fan is running
- As soon as you touch the recirc button… you lose heat

I am assuming this is some sort of fault condition? Something wrong with the flap/recirc function?

When the heater isn’t working, and you push the recirc button, you hear a couple of vacuum thuds from behind the dash, but I don’t get heat. After probably 10 mins the light on the switch goes off.

Any ideas?

Thanks for your help 

Ryley
 

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Premium Member
560SEC, 190E, Frontier, 240Z
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1,329 Posts
Wish I knew more about your system.
The Recirc function does have a ~10 minute timer function in it (for some modes), so that is normal.

The water valves are cheap, might be worth replacing anyway.
 

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1993 300TE, 1995 E320 Wagon
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1,895 Posts
I'd definitely recommend replacing the two valves-- I had tepid heat at best until I replaced my (mono)valve. Be sure to seat the valve carefully before closing the top of the little box though-- In my case it was a subtle difference between fully seated and appearing to be so. Had to do it twice because I had done it wrong the first time.

As to the electrical issues, you may find that things straighten out once the valves are doing their thing correctly. Otherwise, check/replace fuses first, then diagnose.
 

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SuperModerator
1986/1990 W126
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14,311 Posts
That is an odd one - the recirc button being on.

In the single wheel systems, the recirc flap will close in the case of very high exterior temps, but only for a certain amount of time.

In the twin wheel system, it doesn't have that capability so there is a fault there somewhere. The only capability it has for the recirc, is to switch it off after a set time. (Depending on exterior temperature, there are two different times it will allow it to stay on recirc for.)

Does the recirc light flash on and off, or is it constant?
 

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'88 500SEC HV, '84 7MA61 Supra, '83 JZA61 Supra
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369 Posts
Discussion Starter #5
Thanks guys...

Will get a kit for the duovalve and take a look.

The light is constant, not blinking. It does turn itself off sometimes though and the A/C fan stops also.

However, last night I had passenger side heat without the light.

Definately some twilight zone shite going on here...
 

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Registered
'88 500SEC HV, '84 7MA61 Supra, '83 JZA61 Supra
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369 Posts
Discussion Starter #6
Thought I'd bump this as I have a few more symptoms:

When the recirc light is on - the auxilliary (Aircon) fan runs constantly.

I have either aircon freezing air (if temperatures are set low) or blisteringly hot air (on one side only)

When the light is off, and the auxiliary fan isn’t running-

I have tepid air.

I have checked the duovalve and they seem to be operating correctly- one would assume this given I can get hot and cold air.

Any help??

Thanks!
 
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