A couple of different A/C Issues

First Issue
Seems that I have a slow leak. Charged it at the beginning of the season and it went empty again in about 2 weeks. Discovered what seemed like a pretty severe leak (could hear hissing) at the low pressure sensor on the accumulator. Replaced the sensor and the hissing was gone. Charged the system again and this time it went about a month before starting to blow hot.

At this point I Got some manifold gauges and found it was basically empty. What I should have done at this point is pull a vacuum but I did not ... just charged it again.

As of today, my static pressure is right at about ambient (100 or so when I checked it but it was hot under the hood / late afternoon). Running pressures are 40 low, 225 high. Again, this is with ambient at 90-100. Do those numbers sound right for this truck? If so, I'll leave it as is for now and if it leaks out again pull a vacuum and start trying to find a leak.

Second Issue
I have what I thought was a vacuum issue with the switch that changes from max A/C to A/C to heat, defrost, etc. I got the vacuum diagram and started checking vacuum. At idle, I have about 15 hcg at the following locations:

1. hose from the manifold, before the T
2. hose going to the reservoir attached to the hood, driver's side
3. hose after the T, hose going through the firewall to the HVAC, 4WD, etc.
4. grey tube that connects to the HVAC vacuum module.

Again, all of the resgister the same, about 15 hcg. So I don't seem to have a leak up to that point.

From there, as I understand it, the vacuum control module applies vacuum to the various actuators for defrost, vents, recirculation door, and floor vents. This seems very hit or miss in practice, especially when driving. In fact, sometimes I can monkey with the dial switching it back and forth between settings and eventually get everything coming from max a/c. Other times no such luck. It will also switch on its own where its coming from quite a bit.

One thing I did notice is that when I took the HVAC controller out of the dash and pulled the orange vacuum manifold (not sure that's the right term but the one with all the tiny vacuum hoses coming in/out of it) off of the vacuum control module, the connection seemed a bit loose. In fact, if I squeezed it I could get the modes to work exactly as they should. But now that everything is mounted back in the dash, the symptoms are back.

Based on the above, I ordered a new vacuum control module. Does this sound like the right way to go or am I missing something else? What should the vacuum be at idle? Is the 15 hcg enough?

Thanks for any input or suggestions.

sounds like you've got a good idea of what you're doing.

on the 1st issue, i wish i could help, but i don't personally know much about a/c systems. i do know that a clogged line or bad seal could cause false full/empty readings. maybe try charging it with some UV dye.

on the 2nd issue. i think you are on the right track... if a new switch doesn't work, the next thing would be to search for a bad vacuum line/actuator.


whats your year/make/model/engine/trans
typically that kind of info at the beginning of the post will get you a quicker answer.

also, if you're '97 or later there is a 97 FSM here http://www.automotiveforums.com/vbulletin/showthread.php?t=630112&page=2 which might have the pressure numbers you need. i dunno, i haven't looked through that section...

Don't know how I missed including the details. It's a 1997 S-10 Blazer.

Leak is most likely the compressor belly o-rings-- vacuum issue is the connections to the vacuum ball and/or check valve is bad..

Leak is most likely the compressor belly o-rings-- vacuum issue is the connections to the vacuum ball and/or check valve is bad..

What should the vacuum be at idle?

minimum of 17 in hg - 20 is normal

That would explain the intermittent issue then. I am.getting about 15.

That would explain the intermittent issue then. I am.getting about 15.

Ok. So my manual says 17 to 22 is normal. I went all the way back to the intake manifold and am still only getting about 16 and a half or so. Which made me worry about bigger problems than A/C. However, I then read that it says vacuum should decrease an inch or so for every 1000' above sea level. I am in Utah at about 4500' elevation. So now I'm thinking the 15 is fine. Which brings me back to the original problem. I also managed to break the brittle PCV elbow when I took it off so I'm off to try and get that part locally. May as well do the PCV Valve while I'm at it. I will then replace the vacuum hoses with new ones but I'm still not convinced if my 15 inches = sea level 19 inches.

Any other ideas if the above does not fix the problem? BTW, my 4WD is out as well so I am 99% certain this issue is vacuum related since on this truck the vacuum T's off to go the 4WD actuator right after it goes to the HVAC.

I've only had the truck for 6 months or and don't know it's history.

EDIT: I *think* have this fixed for now. Based on the above, I did the following:

1. Disconnected the vacuum hose that T's off the HVAC one and goes over to the 4WD actuator and capped the T connector. Figure I'll address one issue at a time.

2. Replaced the vacuum hoses from the valve cover to the check valve, the check valve to the vacuum ball, and the check valve to the hose that goes through the firewall.

3. Replaced the check valve itself.

4. While I was at it I replaced the PCV valve (and managed to break the elbow and the cab that connects to the valve cover with the vacuum connectors on it but that is another story.

6. Replaced the HVAC vacuum controle valve that is inside the HVAC control head.

As of now, everything is working right ... but that is sitting in the garage. We'll see how it does on the first few trips out. Of course, I still need to track down the 4WD issue. I wonder if there is a leak somewhere down that line that was at least partially causing this.




Thanks.

hope that tracked it down! thanks for posting your steps.