I read the other thread and am staying well clear.

1998 3liter 6cyl XLT 60k mi, 3 months new to me - A/C worked great when I bought it but I didn't check heater. Now that it's cold it blows virtually no heat. It's 40F outside, I just drove ten miles, for these conditions:

Engine heat gauge is a tad below midrange
Heater control is at defrost (or any non-A/C position)
Checked for adequate water in cooland reservoir tank (1-2")
Upper large radiator hose is hot
Heater hose into firewall (bottom) is hot
Heater hose from firewall (top) is cold (goes to heater valve)
Heater hose on engine side of valve is cold
No vacuum at heater hose valve
So apparently there is a interior valve which is impeding water flow into the heater core
Or heater core is plugged
A/C compressor keeps cycling while I'm checking altho A/C is turned off! WHY?

I went to see my mechanic who suggested the heater core was clogged. He said the best fix was back flushing the heater core. And to be careful NOT to back flush the engine back as the crap kicked loose would only serve to clog the radiator in a few months time.

So, I went to my Ford quick lube shop who did the deed of heater core only b/f. Now I have hot air!! And I have antifreeze in the truck with the winter coming on.

Plus I have an oil change and list of things they spotted needing work. That's the advantage of a quick lube at the Ford dealer, they know their goods.

heater core is clogged, doesnt take much to clog 'em.. simply remove heater core hoses where ever the easiest place, inlet and outlet, flush with a water hose by just simply holding the 2 hoses together by hand or with a nozzle .... flush it hard and for a few minute the switch direction of flow until water is clear...

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

Thanks, Terry. I've not had a heater core clog before and I'm happy to know now how to unclog it. That Kodak Easyshare camera does a great job (or did in 2008 when you took the picture).

lol, yw, I snatched the pic off google mine has clogged up twice, even after complete system flushes.. must be core corrosion,, it will get a new core this spring

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

Hey,

I have very light heat in my 99' 2.5 ranger. i found a broke vac hose going to my heater valve. i cut the end clean and re-attached it. but still no heat nor any vacuum on that hose. Do i need to follow it under the fender and replace it? i have decent vacuum on most hoses and very light vacuum going to my egr valve ( disk). not sure if that pertains to this issue or not. any advice would be greatly appreciated. also my ac clutch kicks on and off all the time

Corrected: hose does have vacuum when max ac is on. which i assume is normal. the top radiator hose is hot and the bottom is warm. the right heater hose is hot and the left heater hose is warm...so im guessing flush the core or try changing the therm. I have read many posts where changing the therm. does not help though

I think it should have vacuum on "off" and "A/C" settings..

CORE:this seems to be common, on the 4clangers, I've had to do it twice. last yr n this yr.... common for the core to get clogged, (must be a corrosion issue) just remove both core lines, and flush with a water hose both directions thru core..

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the vacuum line is only for closing the valve, inspect it and make sure it is open.
example: diaphragm "in" is closed, "out" is open.. you should be able to move it with your finger.
A/C clutch: works on all setting to circulate the systems oil.. I dnt think it runs the compressor on "vent" only

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

The valve is out at all times it seems. even when max ac on. it only goes in if a push it in. then it pops right back.

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UPDATE: flushed the core and clean water came out both sides. I am no mechanic at all. so any info would help. It may end up being the thermostat. Should i have air blowing into the engine compartment from that air box against the passanger side of engine ? it is a box that looks to be snapped shut and has an ac line running into it

then try t-stat,

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..

I know this is repetitive as TDMiller has said largely the same things but if you're desperate a rewording of the issue might help.

I'm confused by the 'in-out-popping' and suggest you remove the valve (2 hose clamps) and look/blow through it insuring water will flow easily with no vacuum. Before replacing the valve, blow hard through that hose both ways to insure you have no other restrictions through the heater core. When you had clean water flowing both directions, it must flow easily.

Feel the upper radiator hose for very hot (uncomfortably hot to the hand) after engine warms up several. That will tell you if the thermostat is ok or missing-some owners remove them when they think the engine is overheating. Without a thermostat the water won't come up to temperature and provide a warm heater. Watch the temp gauge and it should stay on cold until the thermostat opens and quickly start it's upward path. The t'stat opening point is usually easy to monitor by gauge and feeling the radiator hose unless it's bad.

No, but are you thinking you have warm air because there is inadequate blower air into the cabin? The flaps which divert air in the cabin from one vent to defroster etc do require good vacuum and won't work if you have a vacuum leak elsewhere. (you did say you had good vacuum above which should make this a non-issue). Air should never blow into the engine area.

could it be an airlock in the heater core?

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I have a 1998 Ford Ranger Extended Cab 4x2 3.0 automatic transmission.