I recently purchased an 86 760 for $300 because it would not boost. After I tightened 2 bolts on the blowoff valve to stop the leaking boost air it runs great. I have found answers to all of the other minor issues it has except for one. When the automatic climate control is in auto it will not start working for around 15 minutes, then it works normally. It works if it is in the defrost position and there is heat within a couple minutes so I know the coolant is warm enough. It acts like the coolant temperature sensor is bad or maybe dislodged from it's mounting and not reading the temperature correctly. Once it starts working in auto it does not quit unless the car is shut off and cooled down. Has anyone had or heard of this issue? Where is the coolant temperature sensor for the ACC located? I found one post that says something vague about it being on the heater core. If so, is it accessible without pulling the core? Thanks.

Addendum from my other post....I just was able to look at my "Climate Units" green book (TP 8707201 Section 8 (87)) which has a great breakdown of the entire ACC system. It verified that the coolant temp "Switch" is mounted in the other heater hose that the coolant flow valve is not. It is close to the valve near the fire wall. It is a switch and not a sensor that 'closes' at 86-104 degrees F. If you have many problems with your ACC you should look for this Green book. They are sometimes for sale on eBay but Volvo still offers them new. Go to the Volvo website and find the book store. Page 235 is devoted to this switch. Good Luck- Scot

Outstanding! Thanks Scot.

I am sure this is obvious to you but you cannot get heat until emgine warms up and hot water flows through the heater core. I don't think the climate control measures coolant temp. There is a sensor for the engine ECU and one for the guage. Both are on side of engine under intake. What is the dash guage showing?

Thermostat working OK?
--
David Hunter

No kidding? I don't get heat until the emgine (sic) warms up? Weird. Volvo thinks that the ACC does monitor coolant temp, I think I'll go with them on that one. I know where the gauge and ECU sensors are, the gauge sender is not used by the ACC if the ACC uses the ECU sensor, it would have to be through the ECU, I do not believe that is the case. Seems to me I would have drivability issues if the ECU never saw the engine temperature. Someone correct me if I am wrong.

For anyone else that has useful input, I found on further reading that the fan runs in automatic if either the coolant temp is above 95*F or the cabin temp is above 64*F. It would appear that the reason my fan eventually runs in auto is because the cabin temp gets above 64* from my putting the heat control on defrost (runs the fan on high no matter the coolant temp). So this further reinforces the idea that the coolant temp sensor is bad. I suppose it could be the ACC module. Am I the only one to ever have this problem?

My 1984 764 had three temp sensors r/t the ACC. One for the outside temp is mounted in the intake plenum above the fan. You can get to it by removing the cowl cover...that covers the wiper motor- most likely not you problem. Then there is the one mounted in the dash behind the mini grill above the glove compartment that has a tube venturi that draws air into it and measures the inside temp. The one you are looking for is actually a temputure switch that is mounted in the heater hose and allows the system to start in auto mode after it reaches a certain temp.- this is near the coolant flow valve behind the engine near the firewall. If you hit the defroster that overrides this sensor. However in auto this sensor or switch needs to reach a certain temp for the system to start in AUTO. Mine was a V6 car but I have looked at several of these over the years and this is what I remember. One guy I knew had a problem with the "programmer" which is nothing more than a motorized vacuum control mounted behind the glovebox. He said he was able to take it apart and lube the motor and valves to fix his problem. In 1988 they came out with the ECC which was a totally different system. However it also had a delay that would wait until a certain temp was reached before the fan would come on and slowly sped up as the temp increased. This is also how your owners manual will explain the AUTO mode. I would think you could "bypass" that sensor and trick the system into thinking there is warm water...Good Luck Scot

Well, the switch is missing. Probably removed sometime by the PO. Does your manual show the color of the wires that go to the switch? I don't see any obvious wires that would have gone to the switch but knowing the color code would be helpful. Thanks.

Andy

I just sent you an email through this site with more info...I hope you got it. Scot

The pictures in the manual are black and white and not close up so I cannot see where they come from or their color and this manual does not have the wiring diagram.However I have an aftermarket PDF of the wiring diagram for 1986 760 and if I understand it correctly the "Heater Fan Temp Sensor" has a white wire coming through the firwall and the other connector was grounded. And my old memory says that these wires came through the firewall in the same grommet that the two vacumm tubes do which should be lower on the firewall but same area side to side as the valve. So the switch is missing and the "T" fitting is plugged? I would have hoped when it was remove they connected the two wires together so as to 'cheat' the system into thinking there was warm water. Scot

T? LOL, that is gone too! I'll go check the wiring again. I did not get an e-mail. I assume it should have gone to the e-mail I used when i registered here. andyrewj44@yahoo.com Thanks for all the help Scot.

Andy

I emailed it again to that address.....Scot