Volvo Maintenance Hints for 7xx/9xx - Bill Garland's Nuclear ...

● Your thermostat needs replacement and your dash gauge is not reading correctly. Cheap
and easy to put in a new thermostat to confirm.
● Your heater core has a deposit of sediment or minerals restricting the flow of warm
coolant in which case the system may benefit from a backflush.
● The heater water valve has a blockage restricting flow and may be in need of
replacement;
● You have a vacuum leak which causes the heat vent control to work improperly;
● Your firewall-side heater water valve was installed backwards; The arrow on the valve
points to towards the firewall inlet, not back towards the engine.
● Control cables from the heater control unit to air mixing doors are maladjusted or broken.
In heater-only cars (no AC unit), the water valve (which is inside the cabin, above the left
footwell) is controlled by a cable from the air mixing door.
● [Pete Fluitman] Check the heater hoses, I have seen several 700's where they are
swapped over and it results in ZERO heat. See the section on Water Valve Replacement
for correct installation instructions.
Heater Won't Completely Shut Off Hot Air.
[Tip from John Sargent] 700 series, with manual temperature selection, have a reputation for
not being able to completely shut off all of the warm air when the manual temperature selector is
fully off. The problem is the flapper door in the heater is not fully closed. There is an adjustment
for this in the cable, just behind the heater control. If you remove the glove compartment, you
can see the heater controls. The cable on the bottom controls the flapper valve for heat. The
adjustable part of the cable is at the heater control. If you see a larger part of the cable, about
3/8 inch and about 2 inches long, that is it. Turn that larger part of the cable until you can feel
the temperature control knob moving off of its left hand stop. You are done!
Heater Core Leaking? [Inquiry:] I guess that the heater core in my 86 740 Turbo wagon is
leaking cause I have antifreeze on the front floor. Is this as nasty a job as it looks? [Response:]
The heater core is a pain in the @#%&* to replace. Try to find out where
the coolant is coming from. Usually if the core goes bad you get a coolant
mist on the windshield with the defrosters on , and you can get some
drainage from the A/C condensate line or onto the carpets. As a
Heater Core for air
temporary fix, you can add a stop leak additive to the cooling system. But conditioned cars
plan on a new core soon. [Tips from Bob] I have done 2 heater cores on
700 series cars. It is rather labor intensive. You have to take apart the
lower half of the dash and partially disassemble the heater case. The
heater core is on the left lower side of the case. You need to remove
radio, fusebox, left side center console panel, bracket that holds fusebox,bottom left side air
distributon box. When you can finally see the heater core, it looks like a hand grenade went off
in your car. If you have done a lot of 700 dash/interior work and are VERY familiar with it, the job
takes about 5 hours. If you are not familiar, plan on a weekend. You MUST have a good shop
manual. I strongly recommend getting the Volvo OEM climate unit manual (see Volvo Technical
Literature.) [Editor] Note that air conditioned cars do not have hoses or a water valve inside the
passenger compartment. Cars with heater only have a water valve on the left side of the