Heater is a pain in the a$$. HELP!

[WVPurpleJimmygirl]

My 4 wheel drive went out last week and NOW i have NO fricken heat!

1996 gmc jimmy

The thermostat has been changed, whole system blown out by air and heat still is bad. Cold air is blowing out, but pressure of air is slow. There is not too much different between med and hi. Got any other suggestions? I really don't want to replace heater core.....

[Cailen]

First, did you have heat before you changed the Tstat?

By "whole system blown out by air" do you mean you tried "flushing" the system with air? If this is the case, did anything come out?

Or do you mean that you purged the air from the system after replacing the coolant? If you haven't purged the air from your coolant system it's possible that air pockets may be the cause of your no heat situation (if you had heat before you changed the Tstat, that is).

If you DID NOT have heat before the Tstat swap, and still don't you have a few possibilities. It may be just that your blending door is stuck closed and no heat is able to pass through. Personally, given that you're not seeing much pass through this is quite likely your case.

It may also be that your heater core is blocked. If you suspect your heater core may be plugged you might try any of the flushing or cleaning strategies listed in the numerous threads on this board. Popular methods are the Prestone flushes or cleans, as well as the reverse flush.

[WVPurpleJimmygirl]

no heat before stat change

tons of sludge came out with air flushing

thats what i'm thinking heater core is block, i don't want to replace it, so you think i should use a flushing agent to remove it.? How does that work. You leave it in there?

[Cailen]

Once your truck is at operating temperature are both lines leading in and out of the heater core hot? Feel em with your hand. If they're both hot then your heater core is probably heating up.

If they aren't you could try backflushing it. There's a really easy way to do it:
-drain a gallon of coolant
-disconnect both the in and out hoses at the heater core
-attach two new 3/8" hoses, one for drain, and one for fill. the drain hose will have to be 4'ish feet long so you can get it over the side of the vehicle.
-take your garden hose and using the pressure nozzle pump a ton of water through that fill hose.

I did this immediately after a Prestone FLUSH. You may consider doing either the flush or the cleaner. The difference is, basically, the flush you add to distilled water and have run through your truck for about 20 minutes of idling (at about 1500 - 2000 rpm). The cleaner you add to distilled water still, but you drive your truck regularly, and after you've accumulated about 6 hours worth of driving you drain it all out.

I would follow up either by a good reverse flushing as I've described. I REALLY don't like those reverse flush T fittings, but some people do so you may consider going that way too. I and other people have found the described method as being very effective.

You might consider removing your rad and backflushing it too. This is a very easy procedure and is described in the Haynes manual.

[the87hyper]

If all kinds of sludge came out, you have the dex-cool sludge. More likely then not your core is clogged. The way i did mine, and it turned out to be very effective is to remove the thermostat, and put the housing back together with the gasket. Dump in some kind of cleaner and run it for a while. I found that if you take the truck for a 15 or so minute drive and give it full throttle through a gear or two it really pushes stuff around in there. I have never had a problem using the T fitting from prestone. Do the back flush like it says on the back of the kit, and you should be in good shape. Good luck

[WVPurpleJimmygirl]

Thanks for all the help, i will keep you posted

[twillers]

Did you loose your heat at the same time as you lost your 4WD? If so, you may have transmission fluid in the HVAC vacuum lines, which may have damaged the actuators that control the various heater control doors. There's a great post from another forum that describes the problem, and the correction.
http://forum.zr2.com/cgi-bin/ultimat...c;f=1;t=004104

If that isn't the problem, and it's Dex-cool sludge, I fixed it by disconnecting the heater hoses from the core, and replacing them with a couple of other hoses, about 4' long. I connected a water hose to one of the two hoses I installed, and ran water through the core. Just be careful, don't use to much water pressure. All sorts of sludge came out. At that point you can connect the water to the disconnected heater lines, and back flush the rest of the system if you want. After that I had heat again.

[dmbrisket 51]

^^^ thank you, took the words from me, even if no atf in the vaccume lines, dont illiminate a Vaccume related problem

[Cailen]

That thread is for 01s-03s. Hers is a 96. If she had a "vacuum related problem" she'd likely have an accompanying coolant leak.

Did you check those inlet and outlet heater lines jimmygirl? Both lines going in and out of the heater core should be hot once the truck is at operating temp.

[WVPurpleJimmygirl]

Hey Cailen one line is hot one line cold!

[the87hyper]

Originally Posted by WVPurpleJimmygirl

Hey Cailen one line is hot one line cold!

Your core is more probably clogged then. Back flush time!! FYI the reason your coolin system is all slugged up is from 1- the factory radiator cap sucks, replace it with a stant. 2- dexcool in the system will sludge up when mixed with regular antifreeze. I'm sure there are other reasons, however these are the only two that i recall. The sludge is nasty stuff, flush the hell out of it and good luck.

[WVPurpleJimmygirl]

Thanks alot, and I will do. Got any sugestions on fixing 4 wheel drive?

[Cailen]

Yeah, heater core clogged. Noticed any coolant leaking in to the cabin on your passenger side carpet? If not you may be in time to flush it.

What seems to be the prob with the 4x4? Stuck in 4hi? Can't shift to 4lo? Shifted to 4hi and now you can't get back to 2hi but you're partially disengaged? Does the thing just not work? Do the lights flash on the switch when you try and shift? Can you hear an audible click? Have you checked the 4x4 fuse? Is your SES light on?

First thing you should do is pull codes. Attach a wire from pin 13 on your OBDII connector by your brake pedal to a good ground source with key in the off position. Turn key to the on position and note the 4x4 switch. Series of flashes denote DTC #s 1-4. If you have no codes the switch will flash once and then go out. If you have one code it will flash 1 to 4 times depending on the code, followed by a 3 second delay, and the cycle will repeat. If you have more than one code the first will flash, 3 second delay, the second will flash, etc, and the cycle will repeat.

As well, check your vacuum lines and shift cable.

[WVPurpleJimmygirl]

4 wheel 4hi and 4 low will not work. The light lights up and makes a clicking noise but won't shift into it. Replaced the vaccum switch and it's getting a lot of vac. pressure but won't work still. No visual signs of leaks

[Cailen]

If vacuum is getting all the way back there then it is likely your TCCM or the shift motor itself.

A code 4 indicates that the TCCM needs replacing. Try pulling the codes.