Auto Parts: Couple questions, chevy s10, cherokee laredo

Question
Anthony,

Thanks for taking the time to answer, I have a couple odd ball questions.  First, do you know where the O2 sensor is on a Chevy S10 2002 4 door 4 wheel drive 4.3 liter V6,  Also on a 1998 Jeep Crand Cherokee Laredo with a V8.  If not not a big deal.

Second questions,  On the CHevy my heat keeps going on and off.  Meaning when I get in the truck I let it warm up and then will turn the heat on high.  About half of the time it responds with hot air.  The other half it stays cold.  I try turning the temp down and back up and that sometimes works.  Also I have tried turning the heat all the way off and then back on and that sometimes works, The worst part of it is that when the heat finally begins to work it will run for about a minute or two and then it turns back to cold, do you know what would cause this and what parts are needed to fix it?

Thanks

Nick

Answer
Well on both cars your O2 sensor will be along you exhaust system..most cars have two 02 sensors one at the exhaust manifold or before catalytic converter and one after..Second answer this would be your heater core or heating unit going out (hence... works sometimes)... only thing to do is replace unit You might get lucky finding unit at Auto Zone being that your car is American Chevy!! Either that or you can try to find one at a salvage yard. I would leave this job up to a mechanic.  Good Luck!