I Have an issue with my heat/ac. When I accelerate the doors in the system change, and the air comes out in a different place. It is due to a cracked plastic tube under the hood, going to the door actuator on the heating/ac box on the passenger side firewall (not sure about terminology). The tubing goes from that actuator down into the taped wiring harness, and I'm not sure where it goes from there. the tubing is very thin and brittle opaque plastic. Anyone know where it goes? I want to replace it if I can figure out where it starts.

Secondly, this may be a separate issue, and is probably electrical. My a/c compressor will short cycle every 15 seconds or so, then finally stay on and cool the cab, but it's totally erratic. I just want to have an idea what I'm dealing with before I take it and have it looked at. Could this be a low freon issue, or does it sound like electrical controls? When it is cooling, it seems to be doing a pretty good job for being 23 years old. Any ideas on either one of these issues? thanks.

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The tube to the actuator is a vacuum supply....

definitely routes to the intake manifold,
but at this time can't say exactly where.


I don't think the compressor short cycle is related,
but it could be a little short on refrigerant.
Usually, on initial startup, a lot of 'freon' flows
while the system is getting balanced out.
Even with no leaks, some porosity in the hoses
will allow small transfer to lose over so many years.

Since it's older, the system MAY have R12, very difficult to
obtain at this point, any only a registered a/c man would be able to
service it, with possibilities that it would have to
be converted to R134 at this time.

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I would start looking at the vacuum lines where they attach to the engine.

My 1984 Furd F-150 has a black vacuum line that comes out of the firewall near the passenger side fender and runs to a small reservior tank with a check valve. I'd check these lines, first, as they are subjected to the engine heat.

Someone here might even be able to supply you with a vacuum diagram for your truck.

I agree with the others on the Freon. You may just be slightly low.

My '84 now runs on 134A, and at idle it gets warm-ish. Take off again, and it gets nice and icy.

Good luck!

Hey guys, thanks for the information. I will do a search and find the connection to the manifold. It's easy to identify, because I believe it's the only opaque (and really thin) plastic line. With that information I can find the connection, leave the old line, and connect a new one between the two points, since the one on there now is wrapped in tape along with the wiring. I will let you know where I find it, and (hopefully) where I find replacement tubing that size.

By the way, if they have to switch it to R134, does it require replacing any parts, or is it just a purge and fill? I will definitely get it fixed, because I am not driving in this 100 plus heat that we keep having in St. Louis !! It's crazy hot here these days. Thanks again

It doesn't require replacing any parts but consider that R134a isn't as efficient as R12 so your system might or might not cool your truck adequately. It's still possible to get R12 (I have some) but it is very expensive (thanks to taxes imposed for no good reason by our stupid government).

I took my truck in and had them replace the R12 with the R134. I believe they had to replace the Schrader valves, and they pulled a vacuum and filled it with the new refrigerant, oil, and some dye, in case I have a leak. It is working great, and doesn't seem to have any problem cooling the cab with the new, less efficient R134. Now hopefully the old a/c compressor will last for awhile. Now, I still need to fix that vacuum line on the vacuum motor on the passenger side firewall. It appears to go inside the cab, probably to the switches on the dash. I was mistaken about the color of the vacuum line. It's actually white, and it's not a big deal that it's leaking, except that when your going up hill or suddendly accelerating, it cuts the airflow off from the dash vents. When you let off the gas, it comes back. For those of you who are old enough, It reminds me of the old vacuum windshield wipers that would nearly stop when you accelerated, and when you let off the gas they would start flying back and forth. Was kind of comical.

Actually there are good reasons for those taxes. R12 is a refrigerant that is very destructive to the ozone. A very small amount can deplete a very large amount of ozone. It is being phased out by an international treaty signed in 1986. Other refrigerants are much less damaging than R12. They could have had a complete ban of R12, but they kept it available longer to service existing systems. The problem is it was often used carelessly, such as recharging a system that has a leak instead of fixing the leak. When it was cheap people didn't care if it leaked, and they kept getting it recharged, and the gas kept getting released. By imposing extra taxes on it it keeps it available for existing systems but encourages it to be used responsibly, such as doing a leak test before a system is recharged.