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MadMikeyL
10-28-2013, 12:08 PM
My 90 SC is only blowing out the defroster vents. So far I have disconnected the harness behind the glove box and determined that I don't have vacuum on any of the hoses on either side. I also checked that the yellow hose directly behind the HVAC control is connected. I also found a post saying that the vacuum source for the HVAC is on the passenger side, so I followed that as much as I could without taking apart my cowl panel, but I could not see where it attaches. If anyone has pics of where the vac source is supposed to be attached so I can verify that, as well as a diagram of what color hoses should have vacuum under what conditions to help me diagnose this, it would be much appreciated. Thanks.

Mike

racecougar
10-28-2013, 08:16 PM
The vacuum supply to the HVAC control passes through the firewall via the same hole as the AC evaporator lines. I can snap a picture later if that will help.

MadMikeyL
10-29-2013, 08:46 AM
I see that vacuum line at the firewall, but then it goes into a group of lines and I lose it behind the return plenum and under the wiper cowl. Before I pull the whole cowl and wipers out, do you know where it attaches to the motor? I also thought about cutting the line there to see if it has vacuum there, and then splicing it back together, but I would prefer not to do that if I don't have to.

Also, the line going through the firewall is black, so does that mean the black line in the connector behind the glove box is the vacuum supply, or is there another connection up behind the dash there somewhere where it changes color?

S_Mazza
10-29-2013, 11:47 AM
If I recall correctly, there are two vacuum trees along the firewall. One is near the brake master cylinder, and the other is more or less right behind the engine. I think it draws from the one in the center.

MadMikeyL
10-29-2013, 02:33 PM
If I recall correctly, there are two vacuum trees along the firewall. One is near the brake master cylinder, and the other is more or less right behind the engine. I think it draws from the one in the center.

Thanks! I will try to trace the vac line to there to make sure it is hooked up to the right spot.

racecougar
10-29-2013, 09:03 PM
Also, the line going through the firewall is black, so does that mean the black line in the connector behind the glove box is the vacuum supply, or is there another connection up behind the dash there somewhere where it changes color?

Yes, the black should be the vacuum supply. As S_Mazza said, it should be connected to the vacuum tree near the center of the firewall in a stock setup. The supply line and those vacuum trees are typically pretty brittle if they're original.

RalphP
10-30-2013, 12:24 AM
Let's add that it goes from the Tee to a check valve, and from there to a "T" or "Y" fitting, and one side goes into the passenger area - the other goes under the passenger front fender to the vacuum canister.

If THAT line is broken under the fender, you'll also have problems with it being mostly up at the defroster.

RwP

MadMikeyL
10-30-2013, 09:03 AM
Well I'm hoping I just have it hooked up wrong or something. I know the heat worked awesome last winter, and I changed the motor in the car at the beginning of the summer, and I never use the A/C, so I first noticed it as it started getting cold, so maybe I either didn't hook it back up, or hooked the wrong line to the wrong port or something. I'll take a look at it probably this weekend. Thanks.

Mike

Plat0ribs
10-30-2013, 10:49 AM
The OE plastic vacuum tubes are heat resistant and discrete (small diameter and shaped to go where you want). However they become brittle over the course of 20 years. Most parts stores also sell rubber aftermarket vacuum hose. I will be replacing all the vac tubes with this during my build in order to avoid vacuum leaks. :cool:

S_Mazza
10-30-2013, 11:53 AM
The OE plastic vacuum tubes are heat resistant and discrete (small diameter and shaped to go where you want). However they become brittle over the course of 20 years. Most parts stores also sell rubber aftermarket vacuum hose. I will be replacing all the vac tubes with this during my build in order to avoid vacuum leaks. :cool:

I have also found that my local parts store carries some plastic vacuum line that closely matches the OEM lines. I have used it a couple of times to replace cracked sections and it worked very well. I think it is Vacu-tite brand (or Dorman, or Motormite or HELP!, which are all the same). They also have a few soft rubber elbows and connectors that worked well. The vacuum tees are functionally fine, though they look a little goofy.

The point is that it's good news - we can have nice tight vacuum lines! :)

RalphP
10-31-2013, 10:02 AM
While replacing, I'd seriously consider steel or copper hard lines for the replacement for the plastic hard lines, and high temp rubber for the joins and where you can't use the hard lines.

Just something to think about.

RwP