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| josephf31 | HVAC question 1991 | ||
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and the fun continues...as I was reassembling the DERM and CCM modules today, I remembered that the AC vents did not blow well, so I pulled the plastic duct and found 2 issues.
1) Main problem, everything comes out of the defroster outlet no matter what the control is on, A/C, heat, etc. The LED lights are on the control head but I hear no "whooshing" vacuum type sounds as you would normally expect. Quick visual inspection on the interior seems to reveal no issues with vacuum or electrical lines, and the 3 "doors" move by hand. Where to start troubleshooting? Could it be a bad control head, servos, vacuum controls,?? 2) I pulled out a few handfuls of insulation(? looks like carpet padding) from the main center vent it was clogging the entire duct. I'm not sure how exactly it got in there in the first place (though I suspect the butcher "mechanic" who messed up this poor car big time) so I am wondering, A) do I need to put this stuff back in? & B) if so, where does it go? Thanks again all you guys are the best! |
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Posted on: 2008/6/18 4:12
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| bogus | Re: HVAC question 1991 | ||
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there should not be any insulation INSIDE the ducts!
The lack of vacuum is caused by a problem under the hood. Check out this document: http://www.corvette-guru.com/uploads/ ... uel_Injectors_LT1_LT4.pdf Page 2, item in yellow circle. I know this is on an LT1, but the L98 should be similar. There is a vacuum port off the intake, near the distributor. Check for a broken hose there, or this thing busted up. |
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Posted on: 2008/6/18 5:02
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| josephf31 | Re: HVAC question 1991 | ||
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Thanks I will check that.
In studying the FSM, it says that this symptom (no air doors moving) could be a defective Heating and A/C "programmer". Does the electronic C68 climate control system use a programmer? I have found reference to a programmer for the manual C60 system... anyone? Thanks! |
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Posted on: 2008/6/18 21:34
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| bogus | Re: HVAC question 1991 | ||
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Yes, there is a programmer on the C68. From my experience, check vacuum sources first. The climate control head unit is very reliable in the later cars.
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Posted on: 2008/6/19 1:41
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| -=Jeff=- | Re: HVAC question 1991 | ||
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if the vacuum lines are good check the check valve under the hood too
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Posted on: 2008/6/20 21:49
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| VtVette | Re: HVAC question 1991 | ||
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Quote:
I'm sorry to hijack Joseph31's thread but I have a quick question for Jeff which is directly related to this thread: My car (as you know Jeff) is a '85 with a swapped in '90+ interior. My car also only blows out the defrost vent no matter what is selected on the head unit. When I hooked the '90+ HVAC unit to engine vacuum I hooked it straight to the plenum. Could a lack of a check valve cause the HVAC to function improperly, thus default to blowing out the defrost vent? I put my car up for sale as well for "whatever I can get" and, well, I guess no one is interested. I was going to buy a C5 'vert but to hell with it. I'm now reinvigorated with new ambition to make my C4 even better than ever! Jeff, what ever became of your '88? |
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Posted on: 2008/6/21 0:43
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| -=Jeff=- | Re: HVAC question 1991 | ||
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Hey VT.. yes, no check valve will cause that, it does not allow to keep 'stored' vacuum in the HVAC. as for my 89.. it is for sale on consignment at a dealer.. not luck selling so far |
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Posted on: 2008/6/22 2:47
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| josephf31 | Re: HVAC question 1991 | ||
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Well the vacuum hoses look OK, although I can't find a check valve under the hood; there is a "T" on the left front fender going from the TPI vacuum source to the vacuum canister in the LF wheelwell, and to the cruise control servo.
Is there supposed to be a check valve in the lines here somewhere, if so where? and if it was missing I don't see how that would make the system get stuck in defrost? In case I do have to replace the programmer, how tough is it? It looks pretty buried up under the dash (though I still have it all apart). Thanks all |
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Posted on: 2008/6/24 14:54
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| runner140 | Re: HVAC question 1991 | ||
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On my 96', its under the passenger side injectors cover. RE: changing the programmer. Pull the seat...up on the fire wall(up from the gas peddle). I'm slow, that was over 4 1/2 hour job. |
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Posted on: 2008/6/24 17:16
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| josephf31 | Re: HVAC question 1991 | ||
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I can't find a check valve anywhere, so either I'm looking in the wrong place, or (nothing would surprise with this car) it simply isn't there.
Would someone be kind enough to maybe post a pic of the darn thing? Thanks all!! |
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Posted on: 2008/6/28 17:43
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| bogus | Re: HVAC question 1991 | ||
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IF you have a check valve, and I am not 100% sure that the L98 actually has one, see post #2, the link included. It has a picture.
Otherwise, there is a vacuum line that runs from the plenum to the interior. If that line is compromised in any way, you loose vacuum to the AC system. |
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Posted on: 2008/6/28 18:07
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| josephf31 | Re: HVAC question 1991 - update and new ? | ||
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Well -- turns out it's not the programmer after all, I ran a test vacuum line from an underhood source directly to the black vacuum host "tee" up under the passenger side of the dash, and now all the doors work as they should!
So -- the problem is, I see a hard plastic vacuum line going into a wire harness which then goes up under the dash, the thing is I can't find under the hood/on the firewall where the other end of that line is! The question is, can anyone tell me where that line comes out underhood and where it connects to a vacuum source? My setup looks nothing like the picture in the link. Thanks all! |
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Posted on: 2008/6/28 20:54
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| bogus | Re: HVAC question 1991 | ||
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yup. I can.
That's the line I was alluding to in my last post. Check the firewall, just to the right of the distributor. The hose comes out with the harness there. It then connects to the back of the plenum, near the distributor, on the right side (passengers) of the engine. |
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Posted on: 2008/6/28 21:21
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| josephf31 | Re: HVAC question 1991 | ||
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Well -- this is driving me nuts, been out most of afternoon trying to fix this darn thing, or maybe I'm just overtired, but for the life of me I can't find the underhood termination of the black plastic vacuum line for the climate control.
I see what I think is the black plastic vacuum line coming through a wire bundle near the distributor, but it goes back down behind the distributor and I can't trace it any further without pulling the distributor. There are 2 vacuum lines on the right rear of the plenum, the rearmost is connected directly to (I think) the fuel pressure regulator. The frontmost goes to a line which connects to a tee which goes to the vacuum canister in the left front wheelwell and the other side of the tee goes to the cruise control module near the ECM. So...either I am not seeing the vacuum line, or it's connected to a different vaccum source (which I doubt since it doesn't work) or (more likely) it's actually broken off somewhere under the hood. Thanks for all of the help so far, any other thoughts, or maybe a pic of a 91 (or 90 or earlier -- the LT1 seems to be different). |
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Posted on: 2008/6/29 0:41
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| josephf31 | Re: HVAC question 1991 | ||
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Apparently the HVAC vacuum connection on my car is totally missing. Not surprising since whoever the prior owner was abuse the poor thing.
Anway, I can see a black plastic vacuum line from the firewall harness going into the mass of electrical wires, the problem is I can't find the other end. So it's either broken or somewhere I can't find it. The FSM is no help here. I have no check valve in sight (or out of sight), would someone with a 1991 be kind enough to post a couple of pics of the plenum source and the check valve (if there is supposed to be one) and most importantly the HVAC vacuum tube and source? I really really really appreciate it, this is like the last thing keeping me from putting her back together and on the road...thanks all!! |
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Posted on: 2008/6/29 21:18
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| bogus | Re: HVAC question 1991 | ||
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I snagged a pic from eBay!
Check for a nipple on the plenum that isn't being used. If that is the case, you have just found a vacuum leak. Otherwise, there are two side by side on the right side of the plenum. One feeds the Fuel Pressure Regulator. Get one of those check valves, a length of vacuum line and get creative.  In the pic above, the nipples in the upper left corner. Those are the ones of interest. The check valve would then split to the canister, IIRC. In general, this is rather basic, complete the vacuum circuit and you will have AC again. |
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Posted on: 2008/6/29 21:33
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| josephf31 | Re: HVAC question 1991 | ||
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Thanks for the pic bog but I need a pic of an installed setup...I have both vacuum intakes coming off the right rear plenum, one to the fuel pump regulator and the other to a plastic tee on the left front fenderwell which branches off the vacuum reservoir and the cruise control module.
The problem is I can't locate the HVAC vacuum feed under the hood, I see where the plastic tube comes out of the firewall near the distributor and goes into a wire bundle, and I've looked under the ECM but can't find a check valve or hose end. I'm sure the previous owner had his butcher "mechanic" work on it and royally mess it up, so I'm still trying to figure it out but a "live" setup picture would be wonderful! Thanks again all |
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Posted on: 2008/6/29 23:56
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| bogus | Re: HVAC question 1991 | ||
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Grand Imperial Pooh-Bah
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Joe,
I just found this pic, I don't know if it will help, tho... The hard line you are looking for comes out of the file wall. Check the picture. The hard line will come out where arrow 1 is pointing. Arrow 3 is the line, arrow 2 is where it is connected. As you can see, on the 87, there is no check valve... I donno if the later versions had one. Attach file:  rightarrowed.JPG (119.71 KB) |
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Posted on: 2008/6/30 0:49
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| anesthes | Re: HVAC question 1991 | ||
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Quote:
I don't see why not. You have done everything anyone could want to do to an '89. -- Joe |
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Posted on: 2008/6/30 11:45
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| hulagan808 | Re: HVAC question 1991 | ||
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I think the confusion with locating where this line goes into the firewall is because it goes along with the wiring through the wiring bulkhead connector, not seperrately.
When I hear of insulation in the ducts I think mice and start looking for chewed anything wire / plastic hose. Aloha |
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Posted on: 2008/6/30 12:16
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| josephf31 | Re: HVAC question 1991 | ||
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Hulagan has the right idea - (I think) I can see where the small rigid black plastic vacuum tube exits the firewall wrapped up in the electrical wire bundle.
From there I see it (staying in the wire bundle) down behind the distributor and somewhere off to the driver's side of the firewall. The problem is I can't find the "other end" of the vacuum line, though I've removed the ECM and checked every inch of the wire bundles looking for a tube exiting the bundle. I have a feeling it may be broken off inside the wire bundle harness, if I just knew where it was supposed to exit I might get lucky and be able to find the end and connect up the vacuum hose/check valve/etc. to get it working again, I'd really rather not unwrap the whole wire harness. Thanks again all! |
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Posted on: 2008/6/30 15:16
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| josephf31 | Pictures? Anyone? HVAC vacuum tube routing for L98 | ||
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Could someone with a 91 (or 89 or 90 L98) please post a few close up pics of the vacuum tube routing on the right rear of the plenum, the left fenderwell, and *especially* any "tee" junctions, if there is a check valve, and, MOST importantly, a pic of where the vacuum tube leaves the firewall near the distributor and connects up?
This is like the last thing holding up my re-assembly and I'm really itching go the her back on the road...thank you thank you thank you!!! |
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Posted on: 2008/7/5 2:05
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| Matatk | Re: Pictures? Anyone? HVAC vacuum tube routing for L98 | ||
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I'll take some tomorrow of my 89. BTW - did you find the connection inside the cockpit? I think it goes to a brake switch to kill the cruise control??? Matthew |
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Posted on: 2008/7/5 2:55
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| josephf31 | Re: HVAC question 1991 | ||
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That would be SO excellent, thanks!!!
The vacuum line to the brake switch for the cruise control goes through the firewall, directly to a male metal outlet on the cruise control module near the ECM... Thanks again!!! Joe |
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Posted on: 2008/7/5 3:16
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| Matatk | Re: HVAC question 1991 | ||
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Unfortunately, I don't think these photos will help you much. I shot what I could see. But I think you already have this covered?
This is the line coming from what I believe is the brake switch - the pic is hard to tell but it is directly under the brake booster and it leads to the cruise control system (next pic)  This is the one line coming in from the brake switch, and another line going back out to the plenum area and it tees off to the vacuum ball in the front d/s fender  This is the line coming from the vacuum ball/cc tee - as you can see it connects with this rubber connector just under the plenum  The line to the left (front of the motor) goes under the plenum and connects plenum which in turn has an outlet that goes to the FPR  The line to the right goes down behind the distributor and enters a corrugated/taped wire harness  I looked through the FSM, but I had a tough time finding a complete vacuum routing diagram. I can look again later. Matthew |
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Posted on: 2008/7/5 4:00
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2002 EBM convertible, Magnusson supercharger, cam, headers, etc. 1989 Corvette...RIP |
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| bogus | Re: HVAC question 1991 | ||
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Grand Imperial Pooh-Bah
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Any luck????
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Posted on: 2008/7/5 6:09
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The single biggest problem with communication is the illusion that it has taken place. - George Bernard Shaw Education is the best tool to overcome irrational fear. - me |
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| josephf31 | This is a huge help! | ||
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The pictures of the check valve look like exactly what I need, thank you!
On my car the vacuum hose from the cruise runs to a tee valve on the left fender, then to the vacuum ball and straight to the plenum connector. I see the black plastic vacuum hose for the HVAC coming from the firewall but can't see where it exits, plus I have no check valve anywhere, from your pics it looks like I'll need to pull the distributor so I can locate the HVAC vacuum tube (I have a check valve I bought from Eckler's). Since it's raining today and I have no garage I hope to dig into tomorrow. Thanks again SO much, hopefully I can figure out where the HVAC vacuum tube is coming out, I think it may have broken off or fallen back behind the distributor (while I'm in there I'll replace the tach filter too!) Thanks again |
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Posted on: 2008/7/5 17:53
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| Matatk | Re: This is a huge help! | ||
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No problem - glad I could help.
Matthew |
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Posted on: 2008/7/5 18:55
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