heater can't keep up

[Sarge1400]

Realized yesterday that my heater can't keep up when it's cold out. Temperature needle is on the 'L', blower fan working correctly, but it just not warming up the cabin like it should. Any ideas?

Maybe related, maybe not, but I also noticed that during acceleration the air stops blowing out the vents. Not really sure if it switches to blowing somewhere else, or just stops, but it definitely changes somehow.

 

[Ishodu]

Sounds like you have a passing T-stat and a possible vac leak. The Coolant might not be getting up to full temp. And the air stopping from the vents is likely a vac leak some where in the ECC system allowing the air flow to switch routes.

 

[sperold]

Good advice^^^^^.
I would start with a new thermostat that has a giggle valve. If not, it is best to drill a very small hole in the one you get. You have a choice of 180 or 195 degree F. Test it on your stove-top to make sure it opens properly before you install it. The big part of the job is to get all the air out after you have installed it, but that little hose to your throttle body is a high point and you may have to let the trapped air out there.
That will do it. There is even a small chance you have no thermostat at all in your engine.

There is a possiblity that your heater core is partially plugged, but it is such a long-shot that I would only start to consider it if everything else fails. That would warrant some kind of a reverse flush by using the heater hoses in the engine compartment.

 

[rubydist]

when you mash on it, if the air stops coming out the vents it will be coming out the defrost - that is the default position for the air position door. that happens when there is a vacuum leak to the eatc. there are many possible locations for this leak, so you will need to track it down.

you could have an issue with the eatc, blend door or blend door actuator, you could be low on coolant, or you could have a thermostat that is stuck mostly open. those are pretty much all the possibilities for the cool cabin temp issue.

 

[intimdatr]

Good info as i think my 89 has a stuck thermostat.

 

[AREA 91]

I agree with the above.

Do the thermostat first.

 

[jimtash]

There's a hard plastic vacuum line with a "t" fitting on the firewall next to the MAP sensor. That supplies the EATC and where you should look first.

Cover up 1/4 of the radiator with a piece of cardboard until you fix the thermostat. It'll bring everything back up to normal temperature.

 

[zak]

If your coolant is low it may be that the heater core is only partially full, which will limit how much heat gets transfered.

Usually when this is the case you'll get better heat output when the engine is reved up (pump will push more coolant around temporarily filling the core)

 

[Sarge1400]

I'm riding in the passenger seat right now, it's 15 degrees out. I've got the EATC sef on 80, panel & floor, fan on high. Can't feel anything blowing on the floor, and very little from the far right vent. Yeah, it's cold over here, no wonder my GF wanted to drive!

 

[rubydist]

this is sort of obvious, but are the vents open? one of my daughters complained that the hvac system 'just whistles' and when I looked at it, she had all the vents closed. maybe the right vent is closed...

you can feel in the air distribution box at the floor to see if something is in there causing no air to go to the right side - its basically a box with an opening cut on the left and right, so no reason that air would blow to the left and not the right unless something has gotten in there to block it.

 

[jimtash]

Look behind the glove box and make sure the distribution hoses are connected.

 

[AREA 91]

I'm riding in the passenger seat right now, it's 15 degrees out. I've got the EATC sef on 80, panel & floor, fan on high. Can't feel anything blowing on the floor, and very little from the far right vent. Yeah, it's cold over here, no wonder my GF wanted to drive!

Crank that sucker all the way to 90 degrees as well.

 

[Sarge1400]

Replaced the thermostat (old one was NOT stuck open), engine temp still doesn't climb above the 'L' on the gauge. Still not a lot of heat in the cabin; I've never owned a Ford that wouldn't cook you if ran on High for a while.

Both heater hoses got pretty hot, though the intake side got hot a lot sooner than the output side. Maybe I'll take the hoses off and backflush the core just to see what happens.

Self diagnostic test on the EATC didn't display any error codes.

 

[intimdatr]

Sure does sound like your heater core maybe plugged up.

 

[hawkeye18]

I agree, you have a blockage in your heater core if there is a substantial temperature differential between the two hoses.

 

[Sarge1400]

Decided to hit some key areas with an IR temp gun after driving home tonight.

Ambient temp: 14F
Upper rad hose: 163F
Heater core intake hose: 124F
Heater core output hose: 94F

I'll try blocking off part of the radiator with cardboard to try to get the engine temp up some.

Must also be a restriction in the heater core. I might try backflushing it, but I have my doubts that it will accomplish anything.

 

[hawkeye18]

Must also be a restriction in the heater core. I might try backflushing it, but I have my doubts that it will accomplish anything.

If you disconnect the heater hoses and take turns sticking a garden hose in each end, you might have better results.

 

[SHOtimer]

I would backflush the heater core.

I would do this by getting two bulk heater hoses and connect them to the heater core, with hose clamps. Then get some hose connections/repair kits from Home Depot/Lowes so that you can connect your garden hose to the end of the heater hose not connected to the heater core. Use your garden hose (under pressure) to flush both ways through the heater core to make sure you have good flow.

This could resolve your problem.

Hows the condition of the rest of the cooling system? A lot of debris? Is it dirty?

You could also have a BDA that isn't fully opening.

Doug