95 RM Heater is intermittent

[Roadmonster]

Hello all, I've read everything here I can find about heater issues with these cars. Thanks to info I found here, I accessed the heater core and tested for warmth. The front/tank portion of the core was hot, but not the interior side. I removed the core and flushed it at my kitchen sink. I got some black flakey crud out of it, but it soon ran clear and didn't appear to have any restrictions. I replaced the core and tested again. This time I got some heat. Today I took the car on a 65 mile trip and nearly froze. Even though the operating temp was normal, I couldn't get anything but cold air from any outlet. Everything shifts correctly from defrost,floor,vent etc.

Here's what's puzzling me; Once I'd reached my destination and shut the car off for 20 minutes, I started it and turned the hvac to Auto. I got some good heat out of the floor vents, but only for a minute or two. The air eventually turned cold. If I trned the unit off, then tried it again 5 minutes later, it would again get a little more heat.

The cooling system is full, everything appears to be working normally, just no heat when you need it. It does seem to work a little better at slower speeds like around town. Highway speeds seem to make it turn cold.

Could this be a vacuum related issue? Has anyone else dealt with this issue and did you find a fix?

['97ventureowner]

Welcome to AF! Sounds like you might have air trapped in your cooling system. When you reinstalled the heater core did you bleed the system? That might be the culprit.

[Roadmonster]

thanks for the reply. I had considered that and checked the overflow tank several times to see if it varied in level. I haven't actually taken a heater line loose to bleed the system, but it's certainly worth a shot. I note that one line goes into the bottom of the coolant reservoir. What's the best way to bleed air out of this system?

[Roadmonster]

never mind on the how to bleed the system question. I found the bleed valve on the thermostat housing. I didn't get any air out, all hoses are hot, heat in the care is not roasting but warm. I'll do more testing. I'm convinced it would do a better job if it didn't have to compete with the AC running all the time and keeping the coil ice cold inside the car!

Thanks

[gn1220]

Do you still have the orange Dexcool in your car? If so you need to back flush the system to clean it all out. Replace with new coolant. What do you mean by the A/C running all of the time? If you have the defroster on the A/C compressor will run. Try turning the defroster off by pushing the "Floor" heat button. Remember the LT-1 is a reverse flow engine when flushing the system.

[Roadmonster]

no orange coolant. I find that the compressor engages and the ac coil is cold in the car no matter what setting the auto controls are in. I understand that they cycle with the defrost etc, but mine seems to run way more than it should.

['97ventureowner]

Originally Posted by gn1220

Do you still have the orange Dexcool in your car? If so you need to back flush the system to clean it all out.

The '95 Roadmaster came with the standard ethylene glycol (green ) coolant. It wasn't until 1996 when GM started putting it in the Roadmasters.