Dash heater / vent / defroster

Less than $25 at Harbor Freight.

rgatijnet1 wrote:
Use the hand held vacuum pump to pull a vacuum and see if it holds as you push the various buttons on the control panel. This is assuming that it will hold a vacuum at all, in any position. With a 1994 vehicle, I would expect that any one of the several vacuum lines could have split and be leaking.

They cant be very expensive. Wouldn't hurt to have one around. Thanks!

Use the hand held vacuum pump to pull a vacuum and see if it holds as you push the various buttons on the control panel. This is assuming that it will hold a vacuum at all, in any position. With a 1994 vehicle, I would expect that any one of the several vacuum lines could have split and be leaking.

Thanks Scott. We're leaving for Myrtle Beach Friday so I probably won't have time to check it before we go. It's a good idea that it defaults to defrost. I can move the actuator manually and the air changes. It's not critical, but I like for things to work right. If I get bored @ the beach, I may tinker with it there.

fuzzbutt wrote:
Scott, great explanation. I had it how it worked mostly figured out. I was assuming the black balls were reservoirs. I found the vacuum controlled actuators also.
I'm hoping when I remove the doghouse cover, I will find a melted vacuum line or something obvious.

If I pick up a hand held vacuum pump, and pulled a vacuum on one of the supply lines to the actuator, it "should" open or close the flap, right?

One of the black balls under the hood, has a normal vac line coming off of it and then there is a real thin line only a foot long or so. Is that normal?

Thanks for the AWESOME help!

fuzzbutt,
Glad I could be of some help here in trying to determine an answer to your issue. So many times folks throw out answers or, what they "think" is an answer to someone issue, when both the OP and others really don't have a concept on how something works before trying to "throw" parts at it or, trying something that is completely off base.

We recently had an issue on the road where we were cruising down the road, in the middle of nowhere (actually quite close to Lordsburg NM), when all of a sudden, no gauges, no speedo, no tack, no cruise control (I was using it at the time) and no exhaust brake. YEOW!!! But, the engine and trans were purring down the road as if nothing was wrong.

Boy, did I learn a lot about how things worked in the next couple of weeks. So, now, I completely (or so I think) understand how all of those gauges etc. operate and how things work. So, analyzing them in the future, might be just a bit easier.

So, as for your vacuum issue, you're certainly on the right track. As for the size of hoses, before and after canisters, valves, controllers, etc. I cannot tell you what should or should not be in place there. I just have a basic understanding of how those systems work. My old (1970) Dodge Charger 440 Magnum utilized that vacuum system for its controls of the A/C and heat system. It had one supply line to the heater/\A/C controls and, as you slid the levers in the control panel, you simply controlled the porting or, direction of flow, of the vacuum to the selected output (ducts, doors etc.)

Now-a-days, it's done a bit different but, the principle operation is close to the same. So, due keep us informed of your findings will you? Good luck.
Scott

Scott, great explanation. I had it how it worked mostly figured out. I was assuming the black balls were reservoirs. I found the vacuum controlled actuators also.
I'm hoping when I remove the doghouse cover, I will find a melted vacuum line or something obvious.

If I pick up a hand held vacuum pump, and pulled a vacuum on one of the supply lines to the actuator, it "should" open or close the flap, right?

One of the black balls under the hood, has a normal vac line coming off of it and then there is a real thin line only a foot long or so. Is that normal?

Thanks for the AWESOME help!

Great explanation FIRE UP. I too am experiencing the same situation.

fuzzbutt,
(like the name) Anyway, yes, this "Phenomenon" is more common than people think. I don't know if you know that much about how the common engine works and how vacuum plays a part but, without going into a novel here, it's simple. If you've ever used or seen a vacuum gauge in action, while driving a car, you'll notice that the more throttle you use, the less vacuum on the gauge there is.

Full throttle usually displays almost "0" vacuum. While an engine is idling, there's upwards of 25" or more of vacuum. So, since many automotive A/C and heat systems utilize what's called "Vacuum motors" on the controls of the heater doors and vent doors etc. (because they're cheap, easy to manufacture and, don't require any source of power) they are effected by a loss of vacuum. And, there's a few reasons they loose vacuum. One, as stated, full throttle, two, a broke or, fallen off vacuum hose, or, problem that happens on occasion, the "vacuum canister" develops a leak.

I forgot to mention, the reason for a vacuum canister. As stated, when at full throttle, there's little to no vacuum in the system. So, when that happens, your statement that said someone told you that the default setting of the control doors in the A/C and heat system is do send the heat/A/C to the defrost, is correct. The reason, in an emergency situation or, in your case, just an incident, the industry standard is for a driver to be able to "see" where they're going due to the defrost working and no other ducts.

Because in the loss of vacuum, those doors can control flaps are spring loaded to aim every thing at the defrost side. Well, when there's little to no vacuum, and you still need heat or A/C at the ducts or feet, vacuum is "stored" in those vacuum storage canisters and utilized, through a series of valves, in that situation. And that stored vacuum is what's used to help control the direction of the air flow during low engine vacuum conditions.

Ok, now that you have a somewhat understanding of the system, then you'll be able to maybe do some investigation as to the loss of vacuum. It's a good move to start with the source of the vacuum for that system. And that's the vacuum hoses etc. right on the engine. If you don't find a faulty, broken or fallen off vacuum hose, than aim your next part of the investigation at the canisters.

I had one, one time that was completely round, about the size of a soft ball. It had a seam that was "glued" from the factory all the way around the middle. Well, by luck, I removed that canister, applied some slight air pressure to it, under water in a bucket and found the leak. I applied some silicone, let it dry and that cured my "no vacuum" at throttle conditions. So, I hope this helps some.
Scott
P.S. Please post what you find out so others may learn.

Spray starter fluid carefully around the vac lines if there is a crack the engine will speed up but be very careful a bad plug wire can start a fire this way easy.