heat

[mad_matt]

i have an 88 s-10 blazer with the 2.8 my problem is when i turn my heat on hi it blows like its on low..also i cant change the vent selection it just comes out al of them

[OverBoardProject]

Welcome to Automotive Forums

The Vent selection is all controled by Vacuum, and all your vacuum hoses probably need replacing by now.
Replace the hoses and your Blazer will probably run better, and the heat controls will work.
An added bonus is better mileage.
Some of these hoses are under the dash, and a little tough to get to. And replace them 1 at a time so you don't have a big problem figuring out where they go to

About the fan, does it make lots of noise sounding like it's working at full speed.
If it's pretty quiet it might be the switch.

[mad_matt]

when i turn it on its quiet like on low....if i have it on while im under the hood there is air blowing out from the blower motor housing could this have anything to do with it??

[old_master]

Try connecting a jumper wire from the battery positive terminal directly to the blower motor positive terminal. This should make the motor operate at high speed, if it doesn’t; you either have a poor ground for the blower motor, or a faulty blower motor. If it does blow at high speed, look for a faulty blower resistor, switch, or wiring problem.

If you're experiencing low air flow, (volume) from the registers and the motor is functioning properly; usually, but not always associated with a rumbling or vibrating sound from the blower, it's possible that mice have built a nest inside the heater housing or blower wheel. If this is the case, the only way to repair it is to disassemble the heater housing and remove the foreign debris. Normally, dog food or fiberglass insulation is what you’ll find. A mouse trap or two, strategically placed, will keep your blower motor running smooth and quiet!

[mad_matt]

thanx ill try running the the jumper in the morning and let ya know

[OverBoardProject]

Make sore that you run an in-line fuse in the jumper

[mad_matt]

ok i ran the jumper like you said and ther is no differance

[old_master]

Matt, You say there's "no difference". Do you mean there is no difference in blower speed or no difference in air distribution? I believe we're dealing with two problems here: 1 blower speed and 2 air distribution. OBP explained about the air distribution issue, and I focused on blower speed. I need a little more data from you to pinpoint the progress, and determine what direction to go with the diagnosis. If you change the blower speed on the heater control, does the blower actually change speeds?

[mad_matt]

Originally Posted by old_master

Matt, You say there's "no difference". Do you mean there is no difference in blower speed or no difference in air distribution? I believe we're dealing with two problems here: 1 blower speed and 2 air distribution. OBP explained about the air distribution issue, and I focused on blower speed. I need a little more data from you to pinpoint the progress, and determine what direction to go with the diagnosis. If you change the blower speed on the heater control, does the blower actually change speeds?

there is no change in blower speed..using the fan controls it comes on on med and when i put it on hi it goes a little faster...as for the selection control whare does the main vac line run from? tia

[OverBoardProject]

It enters the cab through the fire wall close to the top middle.
On the inside it'll take a little time on your back under the dash tracing the lines.

When I worked under here I had the seats out and it wasn't as bad.

I would seriously take the time, and effort to replace all the hoses under the hood as well. They're probably 18 years old , rotten and leaking in a few places. You'll get better mileage, your truck will run better and it's 1 less headach to worry about later

[old_master]

The vacuum line is a black, hard plastic, about 1/8" in diameter. The line runs from the intake manifold to the firewall, through a rubber grommet to the interior. Once inside, it runs to the HVAC control. There are several other lines attached to the control in the same connector. Each vacuum line is a different color; each color represents a different HVAC function. Each line is connected to a blend door in the heater case, and each one has a separate function for directing air flow to the various registers. The most common problem is the plastic line under the hood dries out, gets brittle and breaks. This causes two problems: 1 engine vacuum leak, rough idle, poor mileage. 2 no control over HVAC functions (air distribution). When the HVAC control looses vacuum it goes to a default mode in which it will put full heat in the defrost mode. Blower speed is not affected by the loss of vacuum.

[mad_matt]

ok ill check that out ty