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Unread 01-21-2014, 09:25 AM   #16
CCKen
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1999 XJ Cherokee 
 
Join Date: Jul 2011
Location: Canton, MI
Posts: 2,199
Quote:
Originally Posted by colton_xj View Post
Well, I had time to dig back into it, but I'm not making any progress.

I've verified that I have vacuum into the cab. Nothing in the engine bay seem to be leaking, though the check valve is shot.

Which check valve, the HVAC check valve or the one at the intake manifold? What did you do about this?

I used my bleeder at the HVAC vacuum port and things move about the same as when the engine is running, which is to say sluggishly. I took apart the HVAC vacuum harness, found that the recirculator line was totally plugged, and fixed that.

Plugged with what? Maybe the entire HVAC vacuum plumbing system is plugged.

The recirc door operates now, but never totally closes. I also found that there's a gap between the HVAC box and the defrost vent, which may explain why I'm not getting much flow through the center defrost, while the side defrost vents are okay.

Bottom line, everything is cycling, but it's sluggish and nothing opens or closes the whole way. There's always a bit of air coming out of the face vents, and the air is always cold or tepid at best.

Sounds like the HVAC vacuum system is plugged (not leaking) and the vacuum available at the door actuators is too low (if this is possible). You might try tapping into the vacuum connection at the Recirc door actuator with your vacuum guage and run the engine with the Mode Selector OFF (see circuit diagram) so that vacuum is supplied to the Recirc door actuator. The vacuum available should be the same as the engine vacuum at idle, i.e., 17-22 in/hg. If it's less than 8 in.hg the door system may not work properly.

I'm trying to go back to square one in case I missed something, so I pulled the hoses and ran water through the core, which came out clean. I also checked the blend door: The motor is working, and I'm able to turn the door by hand.

Honestly, I'm at my wits end with this thing, but I don't want to pay a shop to retrace all my steps. I may just start looking for a salvage HVAC box.

In the mean time, any suggestions are welcome. I really appreciate the help.
Try this and see what you get. If the system appears to be plugged, it may have to be cleared.

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Unread 01-21-2014, 10:53 AM   #17
colton_xj
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1999 XJ Cherokee 
 
Join Date: Oct 2012
Location: Denver, Colorado
Posts: 9
Quote:
Originally Posted by CCKen View Post
Quote:
Originally Posted by colton_xj View Post
I've verified that I have vacuum into the cab. Nothing in the engine bay seem to be leaking, though the check valve is shot.
Which check valve, the HVAC check valve or the one at the intake manifold? What did you do about this?
This was the one at the intake manifold. Turns out I don't actually have one at the HVAC tap. I'm going to try to pick them up at a dealer on my way home tonight.

Quote:
Originally Posted by CCKen View Post
Quote:
Originally Posted by colton_xj View Post
I used my bleeder at the HVAC vacuum port and things move about the same as when the engine is running, which is to say sluggishly. I took apart the HVAC vacuum harness, found that the recirculator line was totally plugged, and fixed that.
Plugged with what? Maybe the entire HVAC vacuum plumbing system is plugged.
Some kind of soot. I had to take out the whole hose, then put a bunch of pressure on it with my bleeder, and it finally gave way as a puff of black soot shot out the other end.

As I mentioned earlier, the actuators aren't cycling smoothly--they actually kind of creak and crack as they move. I wonder whether they've started to corrode on the inside and have sent a bunch of junk down the vacuum lines.

Quote:
Originally Posted by CCKen View Post
Quote:
Originally Posted by colton_xj View Post
The recirc door operates now, but never totally closes. I also found that there's a gap between the HVAC box and the defrost vent, which may explain why I'm not getting much flow through the center defrost, while the side defrost vents are okay.

Bottom line, everything is cycling, but it's sluggish and nothing opens or closes the whole way. There's always a bit of air coming out of the face vents, and the air is always cold or tepid at best.
Sounds like the HVAC vacuum system is plugged (not leaking) and the vacuum available at the door actuators is too low (if this is possible). You might try tapping into the vacuum connection at the Recirc door actuator with your vacuum guage and run the engine with the Mode Selector OFF (see circuit diagram) so that vacuum is supplied to the Recirc door actuator. The vacuum available should be the same as the engine vacuum at idle, i.e., 17-22 in/hg. If it's less than 8 in.hg the door system may not work properly.
Quote:
Originally Posted by CCKen View Post
Try this and see what you get. If the system appears to be plugged, it may have to be cleared.
Thanks, I'll give this a try tonight.
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Unread 02-11-2014, 09:20 AM   #18
colton_xj
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1999 XJ Cherokee 
 
Join Date: Oct 2012
Location: Denver, Colorado
Posts: 9
Sorry for the slow response; garage time has been hard to come by recently. I did test the vacuum at the recirc door, and it's getting enough suction.

I finally gave in and pulled the whole HVAC box out so I could see what was going on. Based on the sounds they're making, the actuators are all incredibly corroded on the inside, which means they will slowly move under vacuum (except the defrost vent, which was completely stuck half-closed), but they won't return to their resting position once it's removed, i.e., they're all half-open all the time.

I bought a salvage HVAC box to use for parts, along with a new heater core, since I'm already in there. Between those, and some time cleaning and de-clogging everything, I should be able to get it running smoothly. I'll post if I run into anything else, but I expect this will do it.

Thanks for all your help running this thing down, guys; I really appreciate it.
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Unread 02-11-2014, 10:21 AM   #19
CCKen
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1999 XJ Cherokee 
 
Join Date: Jul 2011
Location: Canton, MI
Posts: 2,199
Quote:
Originally Posted by colton_xj View Post
Sorry for the slow response; garage time has been hard to come by recently. I did test the vacuum at the recirc door, and it's getting enough suction.

I finally gave in and pulled the whole HVAC box out so I could see what was going on. Based on the sounds they're making, the actuators are all incredibly corroded on the inside, which means they will slowly move under vacuum (except the defrost vent, which was completely stuck half-closed), but they won't return to their resting position once it's removed, i.e., they're all half-open all the time.

I bought a salvage HVAC box to use for parts, along with a new heater core, since I'm already in there. Between those, and some time cleaning and de-clogging everything, I should be able to get it running smoothly. I'll post if I run into anything else, but I expect this will do it.

Thanks for all your help running this thing down, guys; I really appreciate it.
You should change the AC Evaporator while you're at it. They do deteriorate and leak after time.

Verify the Blend-Air door is in good condition while the Unit is open and moving freely after you close the Unit up, and before reinstalling it in the vehicle.
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