Which is it failed Heater control valve or bad vacuum???
06-23-2010, 11:01 AM
#1
Rennlist Member
Thread Starter
Which is it failed Heater control valve or bad vacuum???
So I went for a nice drive last weekend with my 93 GTS and found myself sweltering from the summer heat. The a/c was blowing cool not cold air.
So I spent last night checking out system pressures and all showed to be spot on. Still I was only getting 68-72 degree temps out of the vents so I assumed it was the heater control valve.
I pulled the air filter box and started the engine turned on the a/c and as i expected the HCV did nothing. So I pushed the lever down and it held in place perfectly. A/c temps immediately dropped to 52 degrees. boy that felt nice. Changing the settings on the dash did nothing and the valve stayed closed. I tried pulling up on the lever and I could not get it to move. I turned off the car and the valve returned to open position. Repeated the process and same thing.
So the questions:
I will run a vacuum pump (Miti-vac) to see if there is a leak or how much vacuum is required to open it. Otherwise whatever insight into this would be helpful.
Meanwhile thanks in advance.
So I spent last night checking out system pressures and all showed to be spot on. Still I was only getting 68-72 degree temps out of the vents so I assumed it was the heater control valve.
I pulled the air filter box and started the engine turned on the a/c and as i expected the HCV did nothing. So I pushed the lever down and it held in place perfectly. A/c temps immediately dropped to 52 degrees. boy that felt nice. Changing the settings on the dash did nothing and the valve stayed closed. I tried pulling up on the lever and I could not get it to move. I turned off the car and the valve returned to open position. Repeated the process and same thing.
So the questions:
- Is this the symptoms of a bad HCV or lack of proper vacuum or something completely different?
- Does the vacuum run off the air filter box which would result in the lack of adequate vacuum resulting in the operation of the HCV I was seeing?
- Where does the vacuum line terminate behind the firewall?
- Can this be a bigger problem than either the vacuum line or the HCV?
- If I lock the HCV in the closed position to obtain maximum cooling until I can resolve the issue and obtain the appropriate parts to do so, is there any potential down sides?
- Where do I obtain a replacement HCV if it is the culprit? I see them on Ebay for around $40 are these correct units? Is there a better option?
I will run a vacuum pump (Miti-vac) to see if there is a leak or how much vacuum is required to open it. Otherwise whatever insight into this would be helpful.
Meanwhile thanks in advance.
Last edited by cobalt; 06-23-2010 at 11:50 AM.
06-23-2010, 11:14 AM
#2
Rennlist Member
Rennlist Site Sponsor
Your HVAC system has a refrigeration sub-system, a temp control sub-system and a vacuum sub-system.
If the refrigeration system is working and has the proper pressures, any lack of cold air is usually one of the other sub-systems.
If moving the heater control valve lever makes a noticeable difference, the valve isn't shutting off the flow of hot coolant. The effect should not be instant, but should show up as a slow cooling of the output air as the heater core cools.
If the change was instant, that almost has to be a change in the temp control sub-system.
The heater valve should be closed when the system calls for max cooling.
Your problem sound interesting, in the same sense as the old Chinese curse, "May you live in interesting times!".
Go to our website, click on the photos to enter, click on the tips link on the side, then Wally's World, the HVAC. The paper there will explain a great deal about how the system works.
We, and the other vendors, sell heater control valves.
If the refrigeration system is working and has the proper pressures, any lack of cold air is usually one of the other sub-systems.
If moving the heater control valve lever makes a noticeable difference, the valve isn't shutting off the flow of hot coolant. The effect should not be instant, but should show up as a slow cooling of the output air as the heater core cools.
If the change was instant, that almost has to be a change in the temp control sub-system.
The heater valve should be closed when the system calls for max cooling.
Your problem sound interesting, in the same sense as the old Chinese curse, "May you live in interesting times!".
Go to our website, click on the photos to enter, click on the tips link on the side, then Wally's World, the HVAC. The paper there will explain a great deal about how the system works.
We, and the other vendors, sell heater control valves.
06-23-2010, 11:19 AM
#3
Race Car
Unhook the vacuum line to the heater valve use a miti-Vac and see if it closes. If it does then see if the air is now cold. This way you eliminated a valve issue. You may have a vacuum issue or blender door or a vacuum leak going to the heater valve. Do this first and move on from that point.
06-23-2010, 11:19 AM
#4
Rennlist Member
Thread Starter
Your HVAC system has a refrigeration sub-system, a temp control sub-system and a vacuum sub-system.
If the refrigeration system is working and has the proper pressures, any lack of cold air is usually one of the other sub-systems.
If moving the heater control valve lever makes a noticeable difference, the valve isn't shutting off the flow of hot coolant. The effect should not be instant, but should show up as a slow cooling of the output air as the heater core cools.
If the change was instant, that almost has to be a change in the temp control sub-system.
The heater valve should be closed when the system calls for max cooling.
Your problem sound interesting, in the same sense as the old Chinese curse, "May you live in interesting times!".
Go to our website, click on the photos to enter, click on the tips link on the side, then Wally's World, the HVAC. The paper there will explain a great deal about how the system works.
We, and the other vendors, sell heater control valves.
If the refrigeration system is working and has the proper pressures, any lack of cold air is usually one of the other sub-systems.
If moving the heater control valve lever makes a noticeable difference, the valve isn't shutting off the flow of hot coolant. The effect should not be instant, but should show up as a slow cooling of the output air as the heater core cools.
If the change was instant, that almost has to be a change in the temp control sub-system.
The heater valve should be closed when the system calls for max cooling.
Your problem sound interesting, in the same sense as the old Chinese curse, "May you live in interesting times!".
Go to our website, click on the photos to enter, click on the tips link on the side, then Wally's World, the HVAC. The paper there will explain a great deal about how the system works.
We, and the other vendors, sell heater control valves.
I will contact you once I figure out if it is the HCV or not. It would be nice if it was that simple a replacement.
06-23-2010, 11:22 AM
#5
Rennlist Member
Rennlist Site Sponsor
The fact that the valve didn't close with vacuum, but was firmly closed with the same vacuum after you manually closed it might mean that the valve was stuck. It might operate fine now - if so, wait until it fails. If it sticks again, replace it.
Let us know if we can help - and I still suggest that the HVAC paper is helpful reading material.
Let us know if we can help - and I still suggest that the HVAC paper is helpful reading material.
06-23-2010, 11:49 AM
#6
Rennlist Member
Thread Starter
The fact that the valve didn't close with vacuum, but was firmly closed with the same vacuum after you manually closed it might mean that the valve was stuck. It might operate fine now - if so, wait until it fails. If it sticks again, replace it.
Let us know if we can help - and I still suggest that the HVAC paper is helpful reading material.
Let us know if we can help - and I still suggest that the HVAC paper is helpful reading material.
Based on what I have observed so far i am leaning towards the sensor circuit. Although this is all speculation at this point and I will check out the entire system now that i have a guide.
Many thanks for the link and providing the info on-line. If I need any parts you will be hearing from me.
