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Heat works for a few seconds, then it's cold

715 views 11 replies 4 participants last post by  DrSayre 
#1 ·
Hey guys, I'm having an issue getting heat from my 99 WJ. It seems to work for a few seconds if I turn it on after I get the engine hot, but becomes cold after 15 seconds or so. I have changed the thermostat, flushed my coolant, and bleed air from the coolant system, but still no heat. Does anybody have any ideas what is the most likely cause at this point?
 
#3 ·
haha both of those were my thoughts so I must be on the right track! I've seen and I think that's my next thing to try.

Ive also wondered if there was an air pocket somewhere. Is there a way of knowing if there is or not? I bleed the air doing After about 25 minutes or so of reving the engine every few minutes, I figured it did everything it needed to do.
 
#7 ·
Maybe a vacuum issue?
Do you hear any doors opening/closing back in the dash when the temp goes cold?

This winter I've been having an issue where I won't get heat until it sounds like a door finally drops. Sometimes I have to jack with the controls back and forth until I finally hear it shut, and then I'll get heat.

But I guess that's the opposite of your problem. lol
 
#8 ·
+1 with ShadowTek

The hvac system uses vacuum so the line and/or storage canister could have a leak.

Another thought is you could have a cracked blend door that is sliding out of place when you turn on the heat.
 
#11 ·
I don't know if it pulls enough vacuum to test with something like propane, but if so, I guess you could try gassing around the control knobs first. It might be where the lines connect to the control knob.

If you remove the control panel and start disconnecting the lines from the knob, be very careful that you don't break any of the plastic nipples off. They're very fragile. I made that mistake once, but fortunately I was in the process of replacing the whole panel assembly anyway so I had spare parts.
 
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