CattleKev

'96 2500 4x4 12valve x-cab
Ontario Canada
My first posting- sorry for any errors.

Driving down the highway, engine is at running temp. and heater is working great. Come to a stop sign and a blast of cold Canadian air hits me. This happens in any vent mode (defrost, floor, dash vents).
Would this be electrical (brake switch) or mechanical (forces from stopping after going 50mph)?????

After this happens I have to re-set the heat by operating all switches (vent selection, fan, and temp.) desperatly trying to warm up!

Please help.
Kevin

phox_mulder

I'd bet it's vaccum related.

Something about coming to a stop sucks enough vaccum out of the system that the blend door opens (or shuts, whichever).

I'd say you have a little vaccum leak somewhere.

Oh, and welcome to the site, take off your shoes, stay a while.


phox

CattleKev

Cold hoses leak, this makes sense.
Does anyone have access to a vaccum piping diagram?
How does one find leaks?
Where is the blend door pipe and actuator located?
Can I force the door to stay in the appropriate position to rule out any other possible causes?

Kevin

Geico266

I would buy a inexpensive vacuum pump and hook into the vacuum system. Pull a little vacuum on the system and see if it leaks. Just start looking for bad vacuum lines, and connections, broken tees, ect. There are several lines on the firewall you can tap into.

Boatnik

I was having vacuum problems last month with my '92. I am not at all familiar with the vacuum system on the second gens. but here is what I did.
I have a cheap plastic one man brake bleeding pump. It is a hand operated pistol grip vacuum pump. I hooked it to a branch line on the booster and pulled a vacuum with it. The gauge on the pump will let you know if there is a leak. IT should hold vacuum without dropping 5"hg for one minute. I next hooked each individual vacuum line to the pump and pulled a vacuum on each. My problem was in the first line off the engine's vacuum pump. It had gone soft at the pump fitting and only needed a little trim. About three inches. The brake booster also leaked past the rod seal and I replaced it as well. I then started the engine with the vacuum pump hooked up to the pressure switch on the wheel well and got a 25"hg reading. The vacuum will fall off a lot when you hit the brakes but should climb back shortly as long as you keep your foot still. If you are in the habit of pumping your brakes because of ice, you may loose almost all vacuum for a brief period if the engine is at idle. This might cause your blending door to close. It will cause my Check Brakes light to come on as that is set at 8 "hg.

MnTom

Your '96 has vacuum assist brakes. I do believe there is a leak causing your problems and one place to look is at the cruise control under the driver side battery. The next place to check is where the vacuum hose is routed through the firewall. You may also be experiencing the same problem as this thread refers to: https://www.dieseltruckresource.com/...ad.php?t=85853
om

TallTom

Check your anti freeze level. sounds like when stopped at stop sign the water pump is not pumping as hard due to lack of rpms. This will let the heater core cool down due to lack of hot water running to it. 1/2 gal low will let you have heater with higher rpms but freeze your feet at stop signs.

Do you have a cold weater front installed on or behind the grille? A simple piece of cardboard will work for a test run.


Tom