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View Full Version : Knocking sound in my Heater/Cooling Unit of my S13


Agent_S13
08-22-2002, 11:58 AM
Hey all-

When I started my car yesterday, I got a "looped" knocking sound coming from underneath my dash (behind the glovebox). I say "looped" because the sound was similar each time, like it would knock a certain way then it would repeat itself. I noticed that when the car is turned off, it stops -- so its only knocking when the engine is on.

I only had to drive a few miles so I put up with it, thinking that it was cuz the car was cold or something. I got off work and when I started the car again, it was still knocking. I went home to inspect it myself. I took my glovebox off and looked behind it and into my dash. Using my FSM, I realized that the knocking was coming from the Heater Core unit/Cooling unit that sits next to the intake behind my glovebox (intake for the circulation unit). I couldn't get into it, but know its coming from there because I can hear a "whirring" noise as something is trying to spin in there (some kind of motor, perhaps?). I can feel it knocking against the unit like its caught on something.

I think its also related to the AC system because there's another box connected to it as well (they're all connected via a the vents) I pulled the fuse to my AC on my driver's side panel and that got rid of the noise -- Does this mean it might not be the heating panel, but instead part of the AC? I would take it out to inspect, but wouldn't that mean having to discharge the AC system, something that I don't know how to do (as well as being illegal)?

The only reason I pulled the AC fuse is to not have the knocking sound while driving around. Will this hurt the car's heating/cooling in any way? (I don't mind sweating it out if it doesn't hurt the car as a temp solution) I still am able to use the fans and defroster which is good. I'm worried that this might cause the car to run hotter (tho with it being less hot, I'm not worried about needed AC anytime soon... tho for some reason SF is always warm in late Sept/early Oct). This is only a temp solution, would taking it to my dealer (which I'm not fond of doing) be the only way to get this completely diagnosed and repaired? I was thinking that I could remove the unit separately w/out having to discharge the AC (I didn't see any hoses going through the unit I identifed in my FSM) and make a quick swap.

Any information people have towards this (yeah, confusing I know... will confirm the part that is broken as well as a part # if anyone needs more info) would be greatly appreciated! Thanks! &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

-Aaron
'91 240sx coupe

dannhctc
08-22-2002, 12:17 PM
Does the knocking sound change as you turn up/on the fan control?? &nbsp;Has the car sat for any extended period without being driven IE: >3 monthes. &nbsp;My car sat for a good 6 monthes without being started and now it has a click/knock when you change between floor/defrost/driver direction, but goes away as soon as you increase the fan power. &nbsp;May not be related, but it's all I could come up with... &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/smile.gif" border="0" valign="absmiddle" alt=':)'> &nbsp;good luck! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/thumbs-up.gif" border="0" valign="absmiddle" alt=':thumbsup:'>

Agent_S13
08-22-2002, 12:47 PM
Hey, wow quick response... so I'll come back w/ more info here --

Car was not sitting.. its my daily driver... it just crapped out on me yesterday. The day before that (Tuesday) it was fine with no problems.

The next that I was going to do was to plug the fuse back in and try to get AC while this thing is knocking. I want to know if its clogging up my AC or if the AC won't work. I can run full fan speed (all 4 speeds in climate control) blowing with no problems when it was making noise and when the fuse was removed. I guess its directly related to the AC itself (since I also pulled the "Blower Fan" fuses as well and left the AC one in)

Any more ideas on this problem? Thanks!

-Aaron
'91 240sx coupe

junia
08-22-2002, 01:12 PM
The same exact thing happened to my silvia. &nbsp;I noticed that it would happen only when I try to switch my fan from the vent to the defrost position. &nbsp;I just figured something was got loose &nbsp;in the system. &nbsp;Does the sound go away when you try to switch between vent, defroster, and heater?? &nbsp;I figured that it was too much of a pain to take my dash out just to fix that so I left it the say it was. &nbsp;The sound would go away as long as I kept it set on vent.

Agent_S13
08-22-2002, 04:01 PM
Junia --- Its on all the time!! That's why I pulled the fuse... it was soo damn annoying. I didn't even have the AC on when it first occurred yesterday morning. I tried turning it on/off, messing with the different fan settings to see if I would get a response, but I still have a few more tests that I will do when I get off work today. &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/confused.gif" border="0" valign="absmiddle" alt='???'>

Still trying to figure it out... but if anyone's got any more suggestions (short of taking everything apart because I start school on Monday), it would be appreciated. Thanks!

-Aaron
'91 240sx coupe

Agent_S13
08-23-2002, 11:05 AM
Update -

I put the fuse back in and started the car.... knocking noise is still there. I turned on the AC and the motor raised the RPM's cuz it realized it had to power my AC but I didn't feel anything coming from the vents (besides the normal air... maybe I should have let it blow out longer?) My MDM is saying that the AC is on, but I'm not getting any AC so I guess its the core that's clogged itself?

Any more ideas?
Thanks!

-Aaron
'91 240sx coupe

Hightuner
09-22-2003, 01:25 PM
I got a s14

and i also got this knock knock

my AC is working tough

when i leave the defrost on i notice a leak of performance ..

ny ideas