Hello everyone, so my problem is i have a 95 s10 blazer, i just refilled the ac with r34? Anyway i never used the ac before until now. when the car is at an idle parked it seems like the ac blows just fine, but while im driving the fan seems to go off and then come back on again. i was on a 3 hour trip so i played around a bit and it seemed when i let up off the gas the fan started blowing, give it gas and it would stop. I did this a few times and the same thing happened. When im driving it go off and then comes back on, it isnt like on off on off. It takes a few minutes for it to come back on. i still feel the cold air fin the vents it just isnt blowing. I turned the heat on and it all seemed to work fine even while driving. Has anyone come across this problem?? I need help!!!

 

Is it the fan or is it the vacuum actuated doors for the HVAC system that are closing? You could have a vacuum leak in the hoses the supply vacuum from the engine to the HVAC and front axle engagement. You also could have a leaky vacuum reservoir that "stores" vacuum when the engine is under load and the pressure difference between atmosphere and inside the intake manifold is minimal.

There are plenty of threads on the vacuum hoses, including one started by me in which I describe the ID and length of the hoses I used to replace my old ones.

 

It is the fan, it works fine with heat on. i tested it tonight with the heat on and it worked fine. I also tried it with the ac on justy setting there and it seemed to work fine. I will have to test it out tomorrow on my way home from work to see what it does.A leaky vacuum reservoir?

 

When vacuum hoses leaked, the HVAC system would be affected by the supply doors opening and closing so that the air would be redirected from the instrument panel vents to the defroster vents. If nothing else, you can test for this to eliminate that being a problem.

 

Thank you, i looked around today after work and i couldnt find any issues with the vacum lines . But im not really sure which ones i should be looking at, i do know the 4x4 in the blazer works. I will have to try and find the threads on the vacuum lines.

 

Yes, it is worth checking those lines no matter what as they will rot after 15 to 20 years.

Did you check if the issue was the fan shutting off or slowing down versus the air being redirected to other outlets other than the instrument panel vents when the engine is under load?

 

So i was able to check to see if the air was being redirected to other outlets and it is. Once the air flow slowed down i felt up on the dash and it was coming out the defrost, i also noticed that while it blows out the front vents it is also blowing down below at my leg out that vent. That seems to be constant, not jut when the front air slows down but at all times. So my question is are the vaucum lines giving me trouble in the dash?

 

Mostly the fault is with the vacuum lines in the engine compartment. The ones under the dash are hard plastic which I've never heard of leaking. There is a main supply line that comes from the top driver's side valve cover that goes to a one-way valve with a tee. On the far side of the one-way valve one of the leads supplies the front axle engagement solenoid with the other going to another tee that supplies the HVAC system and a vacuum reservoir in the fender.

If you do a Google search for "Blazer vacuum hoses" you will find several links with information. Here is one that has a pretty good picture: https://blazerforum.com/forum/2nd-ge...41/hvac-84946/

What happens is that the lines will rot and start leaking. Even if they look good, they can have a crack or can leak at the nipples for the connectors. What also happens is the connection to the vacuum reservoir can come off. When I replaced my hoses, I added zip-ties as "hose clamps" to keep them in place. Getting hose on the nipple of the vacuum reservoir can be a pain. I used an inspection mirror to help me. It is a cheap repair and well worth doing.

Here is a thread I started to report the lengths and IDs of the hoses I used to replace the vacuum lines. It also has another good diagram of the vacuum lines.
https://blazerforum.com/forum/2nd-ge...replace-95425/

Hope this helps!

Good luck

 

I looked at the diagrams you mentioned and it doesnt look like what i have. The vacum line you mention about going into the reservoir in the fender, mine goes into a plastic ball attached to the hood. I also only have one tee and one check valve. I dont see any hose that isnt connected,I never saw a vacuum solenoid either.

 

There are differences from year to year. Some don't have the vacuum solenoid valve and some have the ball for the reservoir. Try looking for a year-specific diagram for your system. However, if everything is hooked up then I would suggest checking the physical condition of each of the hoses. They can dry rot and not hold vacuum.