Ok I wouldn't be complaining but it COLD out! This is my situation when iam driveing the heater puts out some heat but at a stop light or sitting still at idle it begins blowing cold air I have coolant and no leaks anyone else have this problem before?
http://www.jeepforum.com/forum/f12/heater-core-219329/. It could be the thermostat sticking. Does your temp guage get up to operating temp at 210? To check the core feel both hoses going into it in the engine bay. They should both feel hot to the touch and about the same temp. You have the smaller blower like mine. I upgraded the blower and replaced the core and now I can cook an egg on the coldest days. If you're looking for a temp fix try resticting the air flow across the radiator with a piece of cardboard.
I had to fix the vac lines already cause of the 4wd my fans work pretty good cause I feel heat when its warmed up and iam driving but iam guessing thermostat ill try that first cause its easy to do how difficult is it to do heater core?
The heater core is easy to do. I post a link that walks you through it. It took me about 6 hours and that was taking my time and doing the blower mod too. You should upgrade your blower motor at the same time. Im telling you it a HUGE HUGE DIFFERENCE!
If you are getting heat going down the road and not when stopped I really don't think its the thermostat I would lean more towards vaccum or the heater control selector not locking into position completly. There are two cables on the back of your climate control dash selector. One that controls the temperture or the heat and the other that selects off, the defroster, floor heat or the vent. Sometimes these cables binde, stretch or the clips pop off causeing the control doors in the heater box to stick half way between, so you may be selecting floor heat but you may also have the vent partially open allowing cold air to mix. So when you come to a stop your rpm's drop, causing your voltage to drop some, allowing the fan motor to slow down and cold air from the vent to mix in with the heat easier. In turn giving you the cold air. Move the control lever around to different positions and see if you notice any change. Also move it to the off position and check to see if the system actually turns off. My 1987 YJ does not remain in the off position because of one of the cables, it will turn off when I hold the switch all the way to the left but as soon as I release it the defroster turns right back on.
Yours being a 1990 I believe still works or a cable system its just a different dash selector setup.
1987 YJ Wrangler with 1994 Electronics on a 1998 4.0L Cherokee Engine
ill check that this weekend i havent had the time to work on it but i bought few things for my jeep this week and waiting for the rest of them to come in but my boss had his truck worked on cause he was having the same problem and it turned out it was the thermostat staying open but ill look at cables first then if that doesnt work ill do thermostat
i would go with a higher tempt thermostat. i had a 180 deg in my cj and this winter after replacing my radiator i couldnt get the heat to rise above 170 deg. needless to say the heat in the cab was nonexistant. i poped in a stock temp 195deg last sunday and now the heat works (as good a stock heat can work in a cj). just my 2cents