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'92 740 No Heat

Wren

Wren

Porkchop Sandwiches
Joined
Jun 29, 2006
Location
Athens, GA
I'm working on a 740 that has no heat. I've verified that the heater valve under the hood is operating properly and it has a good thermostat/engine up to temp, etc.

My understanding is that there is not a hot water valve inside the cabin, only the one under the hood and that the hot air is routed into the cabin when a flapper swings open or closed via a servo motor. Is that correct?

Any tips to getting this thing working again? I'm not looking forward to pulling the dash, but it may come to that if needed.

Thanks.
 
I can tell you that on my '85 w/ simple heater-A/C control (not the fancy climate control version) that the heater valve is in the engine compartment against the firewall roughly in front of the accel. pedal. The valve is normally open, only closes when Max A/C is called. So the (normally open) valve allows hot coolant to constantly circulate thru the heater core. Cabin heat is actually controlled by the damper/diverter door, which operates by vacuum.

Car suffered from poor heat twice. Once was after I added radiator stop leak trying to fix the leaking heater core. Heater core ultimately had to get replaced, but the stopleak episode clogged the heater valve, not letting any coolant thru.

Other time was from a failing engine thermostat. It was stuck open, so the engine struggled to reach operating temp. in the winter.
 
I think I'm going to have to pull the dash in order to get to the servo motor that actuates the door flap. I pulled the instrument cluster, but can't get to it.
 
What? Pull the glove box and it's there on the left. Here is a pic of the rod that connects to the hot or cold blender flapper.. Older 740's have a wire that opens closes, the later ones have the electric motor that opens and closes. Look at the green books for your specific one. Also the automatic climate control ones are different as are the 760 ones. But yours should be like my 91 740 with manual controls.

IMG_43741_zpsumcygn3q.jpg
 
Thanks, Simon. I'll take a look through the glove box opening and see if mine matches up to yours.

This is a photo of the CC head, which I believe is not automatic, but manual.

IMAG3143_zpsqgntppiq.jpg


Does your system match up with this Volvo image showing a '92 740 system?

GR-62442.png
 
Update: It was a bad blend motor. I pulled one out of a '91 940 junker that I have and that cured it.

Thanks, Simon! I owe you.
 
Yes that is it. The most common setup from 1990 or so on most 740's and 940's with AC. THey all had AC seems like in USA. I had to look through the green books myself to figure it out when mine did the same thing. There are a bunch of different ones depends on year and model and AC or not.
 
Doesn't go bad that often. I am not really a 700 guy and hadn't changed that many, so I didn't want to say anything, but my memory was exactly as simon posted "take the govebox and some stuff out of the way, no big deal."

I've only ever seen one 700 without air and it was gray market and an '85 744 no sunroof and manual windows. Kinda neat.

'83 and '84 cars usually have all the toys being 760s and they made 240 turbos/260 at the same time, and 260/240T was already crazy expensive, 760 was supposed to be a model above even that! Euro ones probably didn't have air plenty of times though, they say it's pretty rare for europe/northern europe especially to get cars with a lot of options for the domestic/semi-domestic market from what friends say from Norway. Power mirrors or A/C were basically unheard of in the 80s, even on the higher model ones over there.
 
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