Heater/ A/C Quandries-

Perhaps I just suck at the search. But, I searched, and came up with a bunch of heater stuff, and then some lift things, and some rocker stuff, etc etc.

OK, req info: 88 MJ 4.0 2WD 5spd AC

Now, I drove the truck to work today (120 mi round trip). I got bored, so started playing with switches and dials and stuff.

I turn on the A/C to see if it would blow cold at highway speeds. It didn't.

So, here's what it does and doesn't do:

The A/C clutch works, and engages
The electric fan comes on
Air does blow out of vents. And it's even somewhat like whatever I've got selected.
The heat selector is really hard to move
When off, in "cool" posistion, heat doesn't come out
When on the highway, in any position, and I hit the gas, the air stops coming out.
Heat works, but same as above.

So, I can only suppose, that while my A/C is prolly low on refridgerant, it's not to the point that it keeps everything from turning on.

However, as for the lack of air when on the gas, I am clueless.

Anyone have any suggestions?

Thanks.

It sounds like a vacuum issue to me. Check for the little black bottle/canister (that's located (from memory) inside the front bumper on the passenger side) for any holes. If that looks ok, check the hose coming out of it and trace it all the way into the firewall. Especially where it passes underneath the battery, where leaking battery residue can corrode and eat away the hose.

This may be a solution, although I'm sure that someone out there has had a VERY similar experience to the one mentioned in your post, so there may be something that I'm missing....

Best of luck with it,

Quarterwave

I thought I'd seen something too.

I have the dumb lil black plastic thing.

It looks good. But I also have a spare, just in case (came with my front clip)

And, the hose looks good all the way back.

Ok, the black cannister looks ok.

The hoses that supposedly run under the battery (really next to in my truck) are also ok.

Where to go from here?

Ok, to revisit an old topic.

I've now started messing with the AC side of things.

I know the heater valve is ok, I can't find any leaks in vacuum lines visually, nor by carb cleaner/change in idle.

Both my heat and AC blow fine, until the engine is under load on the highway. Or, I should say that I get air from the dash vents, with a little on the floor until it's under load on the highway.

At that point, the dash vents fade, and air comes through the defrost vents with MORE air coming through the floor vents.

I've been looking at the FSM for a while now, and my eyes are starting to go cross. However, it would appear from the vaccuum diagram that the defrost and floor doors are going to partial vacuum.

It also has troubleshooting, which says
"A/C air flow stops on acceleration"
*Defective vacuum storage tank
*Vacuum line seperated or defective
*Vacuum switch defective
*Vacuum leak

While my airflow doesn't stop, this is the closest thing I've seen in the FSM to what I'm seeing.

*Well, I think my storage tank is ok (that is the black tank in the bumper, right?) I've visually inspected it, and the spare I have. I've tried applying vacuum to them, and they seemed to hold. (I sucked on a tube, ok??)

*I beleive my vacuum lines are ok.

*I don't know where the vaccuum switch is. Is that the actual swtich in the dash?

*Where else could I have a vaccuum leak, if not under the hood?

I've done a search, but have yet to see the same problems I'm experiancing. I did only go back like 5 pages, and I might be searching for the wrong words... but still, didn't see it.

So, is there anything else inside the vehicle that might be leaking vacuum? Where is the switch? TIA

btt for the night crowd

For a start, being an 88 and no spring chicken I'd replace EVERY vacum line you got, en mass. Had to do this with our 89YJ, bought boxes of vac line and fittings and then just went to town replacing every vac line I could find. Some were cracked, split, couple were heat melted around the carb. When I was done the vac system worked again as well as 4wd as it had a vac disconnect diff.

Yeah, I keep debating doing that.

I guess there is nothing inside the truck that might be leaking vacuum?

I seem to be having the same issues in my 99. nearly exact same symptoms.
Could you share the outcome of your delemma, and what you had to do to fix it?
TIA
Aaron

over2land said:

Yeah, I keep debating doing that.

I guess there is nothing inside the truck that might be leaking vacuum?

Click to expand...

Hmmm, the vaccuum lines (and fittings and diaphragms) that controll the A/c and heater controls, flap doors, valve, etc. Also the brake booster but thats usually easily noticed. You may be better off getting new lines and testing the other components. Vaccuum lines are a R-PITA to trouble shoot, plus I'm of the opinion that spraying carb cleaner around isin't going to do anything besides introduce flammable solvents to places you don't want them. Also theres propane gas but odds are if the leak is small, intermittent (appears under high vaccuum situations like decel) spraying it won't do anything to the idle.

I would look at vaccuum brake bleeders/vaccuum testers (hand operated pump w/ gauge, a useful, inexpensive tool anyway) youll need one if you ever swap a master cylinder. Also test vaccuum operated systems for leak down.