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While checking my Oil pressure sensor send unit I removed my distributor cap. Later that evening I tried using my heater and it seemed as if the top vents weren't blowing much out and only at ambient temperature. The heater worked fine prior the work mentioned.
After some research one of the suggested areas to check was vacuum leaks. I started looking at areas that I could have jarred or disconnected while working on the distributor. It turns out there is a check valve hose next to the distributor and when I followed the path it led to a "T" connection. One connection went to the vacuum canister and the other was dangling, connected to nothing.
Question:
Where does the loose vacuum hose connect to? It appears like it connects to the power booster but I couldn't find any documentation supporting this except for a Chevy Blazer schematic using that vacuum valve.
I included some photos (borrowed one) to help explain my question.
OP's car I believe is an '89 and the MC caps seem to confirm. The booster looks like a REMAN and the check valve was likely an included piece from the supplier. I'd think that needs capped. The dangling vacuum line for an '89 I don't know (first hand) but maybe WW will slip-on by and recognize it.
OP - is there actually a vacuum "pull" on the "dangler"?
My C4 is a 1989 coupe. I tried connecting the "dangling" vacuum hose onto the brake power booster check valve but it will not fit. The booster check valve is larger than the vacuum hose.
There is definitely vacuum at the end of dangling hose. I've tried looking around areas where the hose could possibly reach at one time and not seeing an open fitting.
I'm thinking of capping off the hose and see if it helps my lack of heat from my panel and floor vents. In any case I can't leave open ended.
My C4 is a 1989 coupe. I tried connecting the "dangling" vacuum hose onto the brake power booster check valve but it will not fit. The booster check valve is larger than the vacuum hose.
There is definitely vacuum at the end of dangling hose. I've tried looking around areas where the hose could possibly reach at one time and not seeing an open fitting.
I'm thinking of capping off the hose and see if it helps my lack of heat from my panel and floor vents. In any case I can't leave open ended.
Any ideas would be greatly appreciated.
Cheers and ride safe!
Ok so whatever happens you have to cap the nipple at the brake booster or figure out what was supposed to be there. Next your hvac system very likely changes modes (defrost, vents, floor) with various vacuum diaphragms and it sounds like it has become somehow disconnected, which is why its sort halfway stuck on defrost. So if everything was fine until you removed the distributor cap then get yourself a flashlight and inspect things very carefully back there and I am sure you will find it .... after all it WAS working fine.
Last - There might be a sticker underhood somewhere, probably near the fan shroud, that has a diagram of the vacuum lines. Many many early cars had this. Hopefully your model year is one of them.
The "dangler" should attach to a vacuum hose that passes through in the vicinity/bundled with the ECM harness. Look at this connector just right of center through the firewall.
I'm away from home right now but will check as soon as I get home. Is the ECM harness located on the drivers side?
Cheers and ride safe!
Originally Posted by WVZR-1
The "dangler" should attach to a vacuum hose that passes through in the vicinity/bundled with the ECM harness. Look at this connector just right of center through the firewall.
I couldn't locate the hose connection you mentioned. I'll have another set of eyes look at it later this week.
Here's an added variable... I was riding around and hit a good size pothole. I didn't think much of it and when I got home looked for the hose connection. When I couldn't find it I decided to block off the end of it in case it sucked debris or such in the engine cabin.
When I tried the heater it was blowing hot again!??? The upper vents had plenty of heat like before. I'm not sure if the bump jarred something loose (like the flap door) or blocking the end of the hose did it.
I don't want to mess with it until next weekend as having a heater for defrost allows me to use the car during the week. I also disconnect the battery before I begin troubleshooting each time. Not sure if it resets anything related to the heater.
Thanks for all the inputs fellas. I have a couple of service manuals that I'm reading trying to understand the heating/AC system.
Cheers and ride safe!
Originally Posted by WVZR-1
The "dangler" should attach to a vacuum hose that passes through in the vicinity/bundled with the ECM harness. Look at this connector just right of center through the firewall.
This picture from Agent 86 shows the HVAC vacuum line (behind the pink distributor power wire) and how it goes into the cabin inside the wiring harness. The right angle rubber part goes on the end of the vacuum check valve:
Thanks for the feedback Cliff. I verified the vacuum line coming from the inside the wiring harness does go to one end of the vacuum check valve. The other goes to where shown below and the other end goes to the vacuum canister and the dangling hose.
I pulled out the resistor module to see if the flapper door would change positions by different climate control settings. It never moved. I tried to physically change the doors position using a long screwdriver and I couldn't get it to budge.
Definitely an interesting situation. Still looking for input fellas if your not tired of this thread already
Cheers and ride safe!
Originally Posted by Cliff Harris
This picture from Agent 86 shows the HVAC vacuum line (behind the pink distributor power wire) and how it goes into the cabin inside the wiring harness. The right angle rubber part goes on the end of the vacuum check valve:
The blend door is controlled by an electric motor. The motor is controlled by the HVAC programmer above the gas pedal, bolted to the firewall on the inside with a 7mm screw. This article has more info:
Thank you for the lead Cliff. I'll take apart the programmer this weekend. Perhaps I have a cold or cracked solder joint as mentioned. I'll check the vacuum lines are secured.
Originally Posted by Cliff Harris
The blend door is controlled by an electric motor. The motor is controlled by the HVAC programmer above the gas pedal, bolted to the firewall on the inside with a 7mm screw. This article has more info:
Happy belated Thanksgiving fellas. I thought I'd close off the question regarding the "dangling" connection. After researching the FSM and the internet it turns out the hose connects to the underside of the cruise control module. The hose had broken off about 1" from the nipple.
I picked up 10' @ 0.59 cents per foot. I will replace the same diameter hoses I come across.
Vacuum hose connection?..
