89 HB with a z24. Blower works fine, controls work fine. But minimal heat output, and I can't really tell if the A/C works. I can't hear the compressor come on and the defrost works half ways. All fuses are OK. I am thinking the heater coil. Any thoughts?
First, make sure the rad is full. Then watch your gauge as the truck warms up, to see if it builds temperature. If not, then check the thermostat, and see it it is stuck open. If it is , replace it.
Ok, the guage doesn't read at all, and I bought a thermostat yesterday. I am going to replace it either today or this weekend, and see what happens. If that doesn't work, what else could be the problem?
I just had this exact same problem. I changed the thermostat and also the fan clutch. My fan clutch was rusted and wasn't moving so the fan was always engaged over-cooling the radiator.
Hopefully you bought a Nissan OEM thermostat. The off-brands supposedly have issues with overheating from what i've read.
Anway, with those two things changed, my gauge goes up to just under half way now and i get good heat. I have a KA24E engine though so my gauge may be different.
If NONE of those things are your problem, it may be a clogged heater core. When you replace your thermostat, flush out the cooling system real well with the heater knobs set to the highest temperature. I even bought a special coolant system flush to get all of the gunk out.