A/C Vacuum leak help request

[sly]

IIRC, I had to replace the Ts themselves in my 88. A smoke machine would definitely come in handy for finding the leaks.

[sxcpotatoes]

IIRC, I had to replace the Ts themselves in my 88. A smoke machine would definitely come in handy for finding the leaks.

In the absence of a smoke machine, would a lit stick of incense suffice, just kind of carefully hold it under the line area and trace the path see if smoke gets sucked in?

[sly]

That might work.

[gadget73]

Know anyone with a vape pen? Those things make massive smoke clouds. I've considered buying one to use for such things. Probably I'd couple it with a small fan pushing smoke through a tube rather than chooching it myself but it seems like you could knock something together fairly cheaply that would get the job done.

[jrhende6]

IIRC, one of the source line Ts goes back out to the thermal blower lockout. You said that was plugged, so there should be no leak there. The other T goes to the cabin air temp sensor just under the dashpad. The line for that one looks to be plugged too. If you plug both of those and also the point of source to the ATC controls, you should be able to pull a vacuum. If that's leaking out, find the leak and fix that and the system will probably work again.

Problem found. You were right.

Problem is with the bi-metalic cabin sensor. Cut the black line to it and plugged it. (Never use AUTO mode anyways. Will black that symbol out too.) Now get vacuum at firewall with barely any leak when pumped to >=15. Still putting it together but am 99.9% sure now. Will come back if not.

Thank you everybody.

[gadget73]

If you mean the in-car temperature sensor that lives above the glovebox, you will need to replace that in order to control the temperature. No vacuum applied to the blend door gives full heat. There is no non-automatic mode in these. The "auto" switch on the dash only refers to the fan speed, the temperature is always automatically controlled via that sensor. Unfortunately they are now out of production so you may be looking at either NOS and possibly NFG parts, or an actual manual conversion that operates the blend door from a cable.

[sly]

If you mean the in-car temperature sensor that lives above the glovebox, you will need to replace that in order to control the temperature. No vacuum applied to the blend door gives full heat. There is no non-automatic mode in these. The "auto" switch on the dash only refers to the fan speed, the temperature is always automatically controlled via that sensor. Unfortunately they are now out of production so you may be looking at either NOS and possibly NFG parts, or an actual manual conversion that operates the blend door from a cable.

This. The black line provides the vacuum to the sensor and the sensor modulates the vacuum to the big fat blend door actuator behind the glove box.
To convert to manual, you would have to either remove the big can actuator (not too hard), then make a bracket to hold the cable that goes to the sensor and mount it on another bar you make to go as far off the other side of the current bar to make it look like a squared up Y. Hooking it on the rod the actuator is hooked on would reverse the temps unless you manage to route it so it can be mounted on the back side of that mess next to the firewall instead of the glove box.

[gadget73]

also just a mention, but if both lines to the sensor and the other end of the line at the blend door actuator weren't connected it will just suck air. If the blend door actuator leaks, it will also do this.

I'm not sure how well a working sensor holds vacuum either, I strongly suspect there is an allowable normal leak rate. If not for the fact it takes a crapload of screws to access, I'd test the one in my car since i know it works like it should. I just don't feel like moving 2 cars and then pulling the dash pad to do it.

[sly]

the sensor is always leaking some through it to the actuator except when it's bloody cold and you have it set on max heat. That should be the only way it holds vacuum.

[jrhende6]

If you mean the in-car temperature sensor that lives above the glovebox, you will need to replace that in order to control the temperature. No vacuum applied to the blend door gives full heat. There is no non-automatic mode in these. The "auto" switch on the dash only refers to the fan speed, the temperature is always automatically controlled via that sensor. Unfortunately they are now out of production so you may be looking at either NOS and possibly NFG parts, or an actual manual conversion that operates the blend door from a cable.

You are right! That big actuator needs vacuum for cold air to blow. So to test, left the black source line to ambient cabin temperature sensor blocked and used vacuum gauge to activate the big actuator. Drove around that way and it blows cold and works like it should. No switching to defrost and warm after 25MPH etc.

I could find a replacement for the ambient temperate sensor and hook that up and let it dangle (since I don't want to remove dash pad). Or I could connect black source line directly to the big actuator. For cold air that will work. Why would this not work anyone?

Also, too much of a headache to convert it to manual as others have suggested.

[gadget73]

Hooking it to full vacuum will make it cold, but you'd need to pull and plug it for heat. People do this when that sensor gives up, and since they have gone obsolete I can't say I don't understand.

[kishy]

Manual is a bit of a job...not immediately possible without some serious hackery. I'm reasonably sure that the entire upper half of the ducting assembly is different between them to accommodate the cable having to operate the blend door in the opposite direction. I think.

If you want to seasonally set it to full cold, you could just put full vacuum directly to the blend door actuator. That'll work. Buys you time to fix it properly later.

Stashing a second sensor inside the dash would work to get you up and running, if you can even find one of the things. It would not work accurately though, as it is dependent on airflow through it, through that little hole below the dash pad above the glovebox, which gets pulled through the sensor by "gentle vacuum" from the blower motor via a tube.

Dashpad removal isn't actually that hard, but I understand concerns about damaging it might keep you away from that idea.

[sly]

You could add a switch to make it a little easier to control...

https://www.amazon.com/Baomain-Pneumatic-HL-2301-V-Position-Normally/dp/B01D2SKOI4/

I actually have one of these installed to control the vent door on my 93. Meant to do the same mod to the 88 I used to have but never actually did it. I still have the switch with 1/8 nipples on it in my stash. Pretty easy to hook up. Put the common port to the actuator and one of the other ports to the vacuum source. Done.

[jrhende6]

You could add a switch to make it a little easier to control...

https://www.amazon.com/Baomain-Pneumatic-HL-2301-V-Position-Normally/dp/B01D2SKOI4/

I actually have one of these installed to control the vent door on my 93. Meant to do the same mod to the 88 I used to have but never actually did it. I still have the switch with 1/8 nipples on it in my stash. Pretty easy to hook up. Put the common port to the actuator and one of the other ports to the vacuum source. Done.

Thanks everyone. Again great suggestions. And the last is rather sly!

[sly]

Thanks everyone. Again great suggestions. And the last is rather sly!

I thought so myself