Intermittent A/C Problem
05-30-2004, 09:08 PM
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Intermittent A/C Problem
My A/C is behaving a little strangely. Everything works fine and blows cold but sometimes, not all the time, under heavy accelleration the center vent starts blowing hot. The system then slowly returns to normal and continues blowing cold. Any ideas on what could be causing this behaviour?? Thanks guys, this is on an 86.5
05-30-2004, 09:25 PM
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This is a common problem. There is a vacuum leak somewhere in your system and as the engine looses vacuum under acceleration the actuators go to their default positions ....
- heater valve on (that is where the heat comes from)
- defroster on (you often loose air from the center vent)
Often the source of the leak is a loose fitting, or cracked hose. Other common sources are leaks in the vacuum actuators. Most shops have "mighty vac's" which are a hand vacuum pump with a gauge. By disconnecting fittings and applying vacuum to them it is possible to isolate the problem.
If you haven't ever changed out the heater control valve, I'd suggest doing that as part of the diagnostics. Other things to check are all the vacuum actuators for the A/C. Remove the package tray under the steering wheel (left drive cars). Remove the trim panel that covers the center dash (beside the gas pedal). You'll see several vacuum lines with color stripes (green, yellow, orange). Disconnect them and check for leaks in each direction ... also listen to hear if the actuators are working as vacuum is applied. If you have a leak in an actuator, a simple fix is to plug that circuit. If it involves the flap that controls the center vent, that flap can be tied open by pulling out the center vent, opening the flap, and using a tie strap around the rod.
It is about a 5 hour (or more) job to replace the A/C actuators in the dash. The shift cover and center dash must be removed along with the radio and other bits. The actuators are riveted into the A/C housing. Rather than remove the A/C housing, the actuators can be split open and the diaphragms can be replaced with those from new actuators.
How might I know? Two out of the three actuators in my '87 S4 were bad. The one that wasn't bad was the air-recirculation control (which is another several hour job for replacement). In addition to hot A/C and air not flowing out of the center vent, my cruise control wouldn’t hold. All of this was due to low vacuum.
- heater valve on (that is where the heat comes from)
- defroster on (you often loose air from the center vent)
Often the source of the leak is a loose fitting, or cracked hose. Other common sources are leaks in the vacuum actuators. Most shops have "mighty vac's" which are a hand vacuum pump with a gauge. By disconnecting fittings and applying vacuum to them it is possible to isolate the problem.
If you haven't ever changed out the heater control valve, I'd suggest doing that as part of the diagnostics. Other things to check are all the vacuum actuators for the A/C. Remove the package tray under the steering wheel (left drive cars). Remove the trim panel that covers the center dash (beside the gas pedal). You'll see several vacuum lines with color stripes (green, yellow, orange). Disconnect them and check for leaks in each direction ... also listen to hear if the actuators are working as vacuum is applied. If you have a leak in an actuator, a simple fix is to plug that circuit. If it involves the flap that controls the center vent, that flap can be tied open by pulling out the center vent, opening the flap, and using a tie strap around the rod.
It is about a 5 hour (or more) job to replace the A/C actuators in the dash. The shift cover and center dash must be removed along with the radio and other bits. The actuators are riveted into the A/C housing. Rather than remove the A/C housing, the actuators can be split open and the diaphragms can be replaced with those from new actuators.
How might I know? Two out of the three actuators in my '87 S4 were bad. The one that wasn't bad was the air-recirculation control (which is another several hour job for replacement). In addition to hot A/C and air not flowing out of the center vent, my cruise control wouldn’t hold. All of this was due to low vacuum.
05-31-2004, 12:51 AM
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Thanks Rich
I've hit the archives and come up with some great tips on checking the vacuum so of I go.......how to explain to the wife I need to spend MORE hours in the garage....
Steve
I've hit the archives and come up with some great tips on checking the vacuum so of I go.......how to explain to the wife I need to spend MORE hours in the garage....
Steve
