Hey guys. I joined this forum to help my mom,
a mail carrier, figure out what the problem is
with the heater in her 98 mercury sable. The
heater is blowing out cold air, especially when
it is on the defrost setting. The fan is working,
but no heat. She has replaced the water pump,
thermostat, a thermostat sensor (if that exists?
)and has also flushed out the heater core.

What do you think the problem is? Thanks in
advance, any help or advice you have would
be greatly appreciated so my mother doesn''t
freeze her mail-carrying butt off this winter! :)

the diverter vent/baffle/whatever it is in that car that controls how much air from the heater core and evaporator (A/C) gets into the ductwork is either stuck, or the actuator has died (vacuum leak) or the vacuum control valve that is part of the A/C controls is malfuctioning... OR you have a vacuum actuated valve on a heater hose that won''t open to allow the heated water through to actually heat up the heater core.

probably a vacuum line or valve problem. There is a lot to inspect. Good luck.

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Thanks for your help :)

Are both heater hoses that enter the passenger firewall hot to the touch?

I''m not sure, I''ll have to investigate that.

Any luck?

My Sable had no heat when I bought it. The heater core was clogged up with sediment. I tried flushing it, but it was of no use because it was so badly clogged. I had it replaced at a cost of about $470.00

Having similar problems on a 99 Sable.
Just changed the water pump and flushed the coolant out really good. Both hoses are hot to the touch.
No heat at all, but the blower does work.

Could it be the thermostat?
I am also wanting to check the vacuum hoses.
Any idea how to get started?

Thanks
Rod

check the vacuum lines to the vacuum solenoids under the dash that control the positioning of the baffles (the parts that direct cold or warm air to the vents). if you''re getting flow through the heater core, then the problem is in the ducting.

That''s what I figured. Problem is, I know nothing about vacuum solenoids. Any links to diagrams or any kind of directions on how to do this?

Thanks,
Rod

I don''t know of any diagrams, but if I run across some, I''ll post them. Someone else may know more. I''m one of those remove things until I find it and put it all back together after I fix it people.

CHances are the core is plugged... They seemed to have some trouble with this.. (Old as 96 and new as 03).. And both heater hoses may still feel hot even though no coolant is flowing through the heater core since there is a bypass between them.. (I''''ve seen people clamp the bypass hose shut to try force some cooling tough) I blame the damn extended life antifreeze, but that''''''''s another thread another time... There is the chance though that the blend door actuator (or something in it''s circuit) has taken a poo... The doors that direct the air (to the vents, floor or defrost) are vacoum, but the temp control is electronic.. Unfortunatly in this cold weather it''s hard to test the blend door but Ford''s diag procedure starts out setting the HVAC to Max A/C with the knob the whole way on cold.. THen turn it to hot and see if the temp changes at all..


With a cloggged heater core what I have done on my 97 Sable, and a few other peoples cars (and this is not probably recomended, but I have had it fix the heat or at least paritally unclog it for some heat)..


Disconnect both hoses from the heater core... You may want to go get a short length of 5/8" heater hose and put on the one spoutof the heater core to make this easier. Step one is to blow all the liquid you can outta the core.. (Air compressor GENTLY, or good ole human power) Then fill the heater core as full as you can with draino (or equivelent) Muratic acid (used to clean hot water and steam heating systems) works even better.. Let this sit for a few hours to render...


After a few hours flush the heater core out THOROUGHLY with water (garden hose connected to the heater core works great) you don;t want the drain cleaner in your engine.. Good idea to flush the rest of your cooling system while you''''''''re at it since it''''''''s probably gunky as well..


Re connect the heater hoses and see what happens.. Worst case scenarios??? THe acid eats a hole in the heater core and it will need replaced, it does nothing and the heater core needs replaced.. Either way it can be worth a shot as these heater cores are not cheap/easy to replace...Edited by: maxfax3

This is just a suggestion, I have a 1989Mercury Granmarquis with the same problem. The way i solve my problem was todisconnect the vacuum hose that goes to the actuator valve and the heat was back. Now in the summertime connect the hose back and i have ac. So i hope this works for you as it did for me.

Hey Max, if the acid eats through the core, then won''t it eat through the dash, other HVAC components, the rug, etc.? And if it doesn''t, won''t you be circulating toxic acid fumes throughout the cabin? I think that is probably not he best advice to be spreading around.

The muratic acid that the average individual can purchase at a hardware isn;t stroung enough to instantly disolve the heater core.. Drain cleaner is somewhat less potenet (do not mix drain cleaner with any acid though, that''ll make some nasty fumes and such!)However if there is a weak spot inthe core andit is under pressurefrom the cooling system it could spring a leak... Usually the equivelant of a pin hole...


Same principal as flushing all the crap out of a cooling system only to have things start to leak (freeze plugs, radiators, heater cores, intake gaskets, ect) The dirt and crud that was in there was keeping the hole plugged....


IF you are usingacid strong enough to disolve an aluminum heater core in a matter of an hour it probaby wasn''t obtained legally.Edited by: maxfax3