Hello, I have a 95 blazer 4x4 that i believe has a leak in the a/c system last year i charged it up ran fine. this year i notice the compressor turn off and on constantly so i figured the r134a was low again so i charged again. one thing i have noticed since driving it that the vent output changes depending on how much i push the gas pedal. at cruising speed or idle air comes out the center vents, under acceleration air comes out the defrost and heat vents, is this normal or do i need to investigate whats going on???
Also i find that running the a/c seems to slow my acceleration down a bit but im still getting the same gas millage as driving without it.

Thanks in advance for any input.

 

The HVAC system modes are controlled by engine vacuum. You need to make sure that the underhood vacuum lines are routed properly, including the vacuum reservoir (ball), and that the check valve is working properly.

 

I checked the valve on top of the transfer case a while ago and the ball was out, not stuck inside pushed on it and it sprung back immediately. sprayed carb cleaner on the lines and intake under the hood while running and no change. i did replace most of the line about a year ago cause they were dried up. I am thinking about capping off the 4x4 side of things and see if there is a difference, does the EVAP system require vacuum? i did get a code for it a good while ago but cant remember the code, and check engine light has not been on since. Also i did have a bad input shaft seal on the transfer case, replaced that and the front accuator was full of transmission fluid so that has been removed and capped off.

Update, i flipped the check valve around thinking it may be on backwards still get same symptoms, capped off the transfer case line still get same symptoms, pulled the storage tank off the hood and i am getting a little bit of transmission fluid out of it, will this cause the storage tank to not work properly? check valve not working right? i wouldn't think i would have a leak in the a/c line going inside the blazer but i guess i could be wrong, anybody got any ideas????

 

Transmission fluid in the vacuum system can cause all sorts of problems. It doesn't move as freely as air does in the vacuum lines which means that it won't allow actuators to function properly if it is in the line. You need to pull the lines, including those under the dash for the HVAC system and make sure that they are clean. A light solvent like simple green can be flushed through the lines to clean them without degrading the rubber. Then blow the lines out with compressed air and put it all back together.

 

Sooo i've got more work to do i hope the hvac line under the dash isn't to hard to get to, thanks for the input i have been scratching my head about it for a while, i just did a coolant flush and oil change and i still got the lower ball joints to replace now ill just add ripping the dash apart to my list fun fun. Thanks again.

 

One more thing, fix the cause of the problem which is a combination issue of a leaking vacuum switch on the transfer case and a leaking input seal on the front of the transfer case. The transfer case needs to be dropped to replace the input seal.

 

The problems at the transfer case has already been taking care of i lost my transmission shortly after the seal went bad lucky me, but i did find a good tranny off ebay for about 700 bucks with shift kit installed torque converter plus extra trans cooler. the switch on the top of the case seems good to me the ball is hanging out like it should be, press on it and it springs back quickly, im not currently getting any trans fluid up the vacuum lines at the present time. i did run some compressed air through the hvac line to the control switch a little bit earlier just to see what happens and only thing i got out at the control switch was air. I think im going to get a handheld vacuum pump with a gauge before i go any further to see if i can pin point whats holding vacuum and whats not.
thanks again Swartlkk

Update. starting testing things with handheld vacuum pump from motor to check valve leaks very little, storage tank fine, 4 wheel drive fine, a/c will not hold vacuum at all, pulled the control **** started testing lines there and the brown line will not hold vacuum, grey line i believe is the input line all the other lines hold vacuum. now time to figure out where the brown line goes anybody got any ideas??????

scratch that!! brown line does hold vacuum when black return line is capped off. the seal at the selector switch is bad.
played around with the switch for a while, stuck an o ring underneath the spring to give more tension, got it to hold vacuum on 3 out of 8 settings, guess i will be looking for new switch.