After Head Gasket repair - no cold A/C or Heat! :(

wolverine9827 said:

Can those small vacuum lines cause all of this? (grumble grumble)

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ForTheLoveOfMonkeys said:

In a word: "Yes". The climate controls for a lot of older cars are completely vacuum controlled.

I'd have to know the year of your truck before I can tell if I have anything of value to offer up to you. But two quick things:

One: did you by any chance remove the A/C lines when you were disassembling the engine to get to the heads? If so then did you recharge/prime the A/C lines?

Two: You say funky... is air blowing from where it should or from defrost only?
I ask because in my truck I redid the head gaskets and everything climate related ran fine for about 2 weeks. Then my everything was blowing only from the defrost vents no matter what setting I chose. Turned out that when I put everything back together a tee on one of those vacuum lines had come too close to an exhaust manifold and melted shut. All turned good when I replaced the fitting and rerouted the vacuum line. (More of an example to how important those stupid little lines turned out to be than an offer of fixing your problem.)

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ForTheLoveOfMonkeys said:

I totally agree with what Craig said, that you've got a vacuum leak. I'd start by figuring out where it is and solving it and then seeing what problems clear up and which ones are left.

Start with the easy ones by tracing the ones under the hood on the passenger side. You can see two of them disappearing into a vacuum control valve that is hidden underneath of your coolant overflow/washer fluid reservoir.

These are common culprits. From the sounds of it seems like you don't have a huge and obvious vacuum leak (it's intermittent from your description) so really look at these lines hard all the way back to where they go into the firewall and behind the engine. You'll be searching for anything out of the ordinary and pay a little extra attention to any fittings where one line connects to another, I missed that on my first go through because it was melted internally so it didn't really stand out until I was running my fingers over it.

If the leak is not in one of these two lines then that valve I mentioned beneath the reservoir is a secondary culprit. Minor pain to get to because you have to remove the airbox and the bolts holding the reservoir in but not too complicated or time consuming. It looks like a black ball.

A shortcut to all of this is the "smoke test". Go out and buy yourself the most smoke producing cigar you can get your hands on and some sort of rubber fitting that will go on a vacuum line and you wouldn't mind putting your mouth on. I'm sure you can see where I'm going with this, remove the air hose that goes from airbox to throttle body, block off the now exposed throttle body with a glove or something, you don't want the smoke to get anywhere near your MAF. Light up the cigar. Take a deep breath and exhale the smoke into a vacuum line, (I typically use the brake booster line on the back of the driver's side). Repeat this several times, any vacuum leaks will show by wisps of smoke rising out, look for those and you can trace them down to your vacuum leak. If you don't see any then it's likely one of three scenarios:

1) It's not a leak so much as an obstruction somewhere in the lines, you're back to hunting it down by visual and tactile inspection of each vacuum line.

2) It's in the cab, if you step into the cab and smell cigar smoke, then it's a leak in a vacuum line under your dash.

3) You've gone and dun messed up somewhere. Try again. More smoke, cheaper cigar.

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