Split orange vacuum line & AC problems

[green55]

The orange vacuum that Ts behind the glove box is split on my Jimmy. The pet that goes through the firewall is completely broken in half. From wiring diagrams I’ve seen, it seems to be the defrost vacuum line. My AC hasn’t worked in my truck since I got it going again but did work when parked. Not sure if this line was broken when parked.

Would that vacuum line being broken cause the AC to not work? Or would it only mess up where the air is coming from? When I try to use the AC now, I hear hissing behind the dash and the engine surges about every 5 seconds

 

[Wes Harden]

It will only mess up where the air is coming from. If your truck sat for a bit, I wouldn't be surprised if the freon leaked out.

you could splice a new hose to the old one if you can find any good part of the orange vac tube

 

[ktmoutfront]

That vacuum leak will cause the surging at idle. Usually just idles fast and rough. That hose does nothing for the AC kicking on. Just supplies vacuum to the control system.

 

[green55]

Interesting -- I didn't realize a vacuum line could be spliced. Any tips on how to do that?

And as far as probably being out of freon, how would I check that? I assume if it is out, I have to figure out what's leaking, fix that. Then, from what I'm reading, sounds like I have to go through a whole thing to get it switched from R12 to the new freon. I know nothing about AC systems...

 

[green55]

Oh - I think I answered my own question with the splicing. Probably supposed to use something like this:

Advance Auto Parts - Down for Maintenance

Still not sure how to proceed with the AC diagnosis though

 

[Wes Harden]

An a/c manifold gauge assembly is a necessary diagnosis and service tool.
electric diagram for 73-80ish.

 

[ktmoutfront]

Every auto parts store has a misc repair section. In there you should be able to find a pack of generic vacuum fittings.

The AC diagnosis can be involved. The best way to convert to R134a is a complete flush, change the dryer and orifice. Then do a vacuum evacuation of the system to check for leaks. It it will not hold vacuum, finding the leaks can be difficult. There are many ways to do it. They make screw on adapters for the recharging the system. You should have someone who knows what they are doing recharge it.

 

[green55]

Thanks y'all. This sounds like something where I should just splice the broken vacuum line myself and leave the rest to someone who knows what they're doing. I can live without AC for awhile longer with how expensive I'm sure this'll be.

Is that "someone who knows what they're doing" generally just a normal mechanic or are there shops specifically for this kind of HVAC stuff?

 

[Wes Harden]

Could be either way. I would check around for reputable shop.
Try running the ac and feel for cold air at defrost vents, post up results

 

[green55]

K will do. I'll check after fixing the vacuum line. I honestly haven't run it very long when testing it because it seemed like a bad idea with the engine surging haha

 

[Wes Harden]

If you fix the vacuum line cold air should be directed out the dash vents.
If the vacuum system fails the air plenum defaults to defrost

 

[88Silverado]

The "surge" you are feeling is probably the compressor engaging and dis-engaging. It engages until the pressure drops to the lower limit and shuts off until pressure rebuilds. This is normal. Several factors affect cycle time (Freon pressures also vary with outdoor temps). 5 second interval at idle "may" be normal for your conditions and freon load. As mentioned, drive it and see if its blowing cold otherwise take it to a good shop for check.

In Ca. you cant get R12 anymore so I converted to R134. R134 is less efficient than R12 so cooling is somewhat less too. This was the first thing I noticed however, I later changed the condenser (in front of the radiator) to a R134 type replacement and now on the open road I can honestly declare a Brass Monkey Alert for the cab and back seat. Its too cold sometimes. Idle cooling is a different story. Where R12 still blew ice cold at idle, 134 does not, especially if running stock fan. Addition of an electric fan helps but I find it un-necessary as im not stopped idling for long periods of time. If I am sitting, just bumping the rpms up to about 1K spins the fan fast enough to cool again.

Good Luck!

 

[green55]

Thanks for the extra info @88Silverado. I should have time to fix the vacuum line this weekend. I need to get under the cowl for find the other end of the line.

Figured since I have to take the wiper arms off to do that, I’d go ahead and replace them since they’re cheap. I’ve tried declogging the fluid holes and lines but can’t get it to come through right, so hoping to kill 2 birds. Been waiting on those to come in so I can do it all together.

Will report back on what happens with idle/ac after that

 

[Blue85]

Simplest diagnosis is visual inspection. Switch the AC on, pop the hood and see if the compressor turns. Some people actually disable the AC by removing the belt or unplugging the wires to the clutch. So check the low pressure switch, clutch connection and fuse. If they're all in place, check with a voltmeter. If there's not enough freon, you won't get voltage past the pressure switch. That's probably where you bring it to a shop.