heater works intermittingly. sometimes yes , sometime no.
blower works fine.
A/C works fine.


what gives?

 

Any chance your coolant is not full, and there is air in the system? If so, top off and burp it....I now own the $20 funnel, but prior, I would have put an old towel around the radiator cap opening, and let some coolant overflow onto the towel...while idling with heater on hot....this is when you believe that the radiator is in fact full...air will cause it to overflow....do this a while then top off once and for all.

 

As already said likely low coolant

 

$20 funnel to prevent air bubbles? Please explain and/or tell me where to purchase. Thanks.

 

It's this one....with it, you can simply let the car run with radiator cap off, and put some coolant in the funnel. The car will expel air a few times, and draw more coolant in. Once you are satisfied that it's done, simply push the stopper in the funnel, and take it away. No waste or spillage, the excess coolant will be in the funnel, and you can drain it into a container.


But without, one can let the car expel air and coolant onto a towel, and refill the radiator.....

 

You need to understand why you are low on coolant (assuming posts above are correct, which I think is right), figure out if you are leaking coolant, and if so fix it, otherwise intermittent heat will be the least of your problems. Its possible the last time the coolant was changed the system was not fully bled and topped off. But, if intermittent heat is a relatively new occurrence, then it is more likely that coolant is leaving the system somewhere. Under that scenario you need to look it over thoroughly for evidence of leaks, including looking at the condition of the engine oil for possible head gasket leak (rather unlikely).