I "WWested" my 84's a/c system

[ganun]

Dave, if you're still snowed in and looking for something to do with the two fans, well you could do the old low speed / hi speed by the old trick of switching them from series to parallel depending on pressures.

[DaveMcKenz]

Thanks, George.
I was thinking about that. I bet I could hook up two relays to do it. Maybe.
Take care,
Dave

[wwest]

Just stumbled across some new info.

For quite some time I have known that the 964/993 series has the ability for "after run", ignition off, ~15 minute engine cooldown period using the cabin heater blower.

Thread I just followed seems to indicate that the '84-88 Carrera's had the same feature, heater blower control module and heater blower fuses have unswitched power. By default that might also supply power to the footwell blowers.

Anyone experience this, footwell blowers running with ignition off, say on an exceedingly HOT day?

~15 minute TDR function inside the cabin heat blower module...??


If this is the case then this would also help to prevent after-run refrigerant over-pressure instances due to rising engine heat post ignition off.

Anyone?

[GH85Carrera]

My 85 heater is not the automatic version and has no sensors of any sort at all. It only comes on when the levers are pulled up.

[wwest]

Originally Posted by GH85Carrera

My 85 heater is not the automatic version and has no sensors of any sort at all. It only comes on when the levers are pulled up.

Your '85 has the cabin heater blower control module even without the automatic aspect.

The top fuse in the engine compartment supplies power to the module, the second one down supplies power to the blower motor.

You probably have never had reason to have the after-run function be enabled, or it happened after you walked away from the car.

It's easy enough to check the automatic engine cooldown functionality.

With the car running remove the connection from the temperature sensor and short it to ground, the cabin heater blower should run even with the heat control levers full DOWN.

If not then it is likely that someone has modified your car.

[GH85Carrera]

I have owned it for 20 years and driven it a lot. It has been in more 100+ heat days than I care to remember. I have come home from a day at the track and parked in my nice quiet garage. Shut the car down and unload the car and there is no noise except the tink tink tink of the exhaust system cooling down.

There is no temperature sensor in the heating system. I have been all over that car from ever angle.

[wwest]

Originally Posted by GH85Carrera

I have owned it for 20 years and driven it a lot. It has been in more 100+ heat days than I care to remember. I have come home from a day at the track and parked in my nice quiet garage. Shut the car down and unload the car and there is no noise except the tink tink tink of the exhaust system cooling down.

There is no temperature sensor in the heating system. I have been all over that car from ever angle.

Thermostatic sensor is placed such that it detects the engine temperature, some said under the intake manifold.

Confirmation:
http://www.pelicanparts.com/techarticles/911_extra_cooling/911_extra_cooling.htm

[Ronnie's.930]

Originally Posted by GH85Carrera

There is no temperature sensor in the heating system. I have been all over that car from ever angle.

But is there a carbon fines sensor/collector/warning buzzer situated someplace?!?!

[SilberUrS6]

Originally Posted by Ronnie's.930

But is there a carbon fines sensor/collector/warning buzzer situated someplace?!?!

Oh, schitt. Here we go...

[wwest]

Originally Posted by Ronnie's.930

But is there a carbon fines sensor/collector/warning buzzer situated someplace?!?!

Do you mean to be the first to take this thread sideways?

[Bob Kontak]

Originally Posted by wwest

Thermostatic sensor is placed such that it detects the engine temperature, some said under the intake manifold.

Interesting info. It does say in your link if you have the manual controls (as Glen has) you can do the lever lift trick but I am reading that the manual set up does not have the after run functionality.

[wwest]

Originally Posted by Bob Kontak

Interesting info. It does say in your link if you have the manual controls (as Glen has) you can do the lever lift trick but I am reading that the manual set up does not have the after run functionality.

I suspect Bob mean to say:

"If you have a pre-84 911 with manual.."

otherwise the article makes no sense.

I have verified that the blower gets turned on if the engine rises to high while the engine is running, grounded the temperature sensor signal.

I have also verified that the module and the blower circuit are powered with the ignition off. '88 Carrera, manual heat.

No actual reason for a decisive conclusion either way.

But then again, that's how the after-run cooldown blower operation works in the 964 & 993

[Ronnie's.930]

Originally Posted by wwest

Do you mean to be the first to take this thread sideways?

Wuts wrong with a fines warning system?!

[crownarch]

Unless I read that tech article incorrectly it states "with car stopped" it does not say with motor off. I have my car setup so that I can manually turn on/off the engine blower anytime by moving the heater levers up and kick on the blower motors or footwell blowers at wish. It will definitely allow you to better control engine temp when in hot/heavy traffic. However, I accomplished this by modifying the blower motor/heater relay in the engine compartment. There is post on pelican that explains how to do this. Hope I am not confusing the issue.

[wwest]

Originally Posted by crownarch

Unless I read that tech article incorrectly it states "with car stopped" it does not say with motor off. I have my car setup so that I can manually turn on/off the engine blower anytime by moving the heater levers up and kick on the blower motors or footwell blowers at wish. It will definitely allow you to better control engine temp when in hot/heavy traffic. However, I accomplished this by modifying the blower motor/heater relay in the engine compartment. There is post on pelican that explains how to do this. Hope I am not confusing the issue.

The article (post # 47) applies to the pre-84 911's

your '87 already had the automatic engine cooldown function.

The module has 2 inputs that enable this function.

A speedometer input, and the engine oil temperature sensor.

My understanding of the operation is that if the car is consistently moving slowly, say stop and go rush hour traffic, and the sensor closes, the cabin heat blower will be powered to help cool the engine down.

I have read elsewhere that the thermostatic sensor switch is mount on the oil cooler mounted to the engine case.

[KelogGes]

Originally Posted by DaveMcKenz

I just want to clarify. My Retroaire system works great in steady state performance. I get mid 30 to 40 degree vent temps in 90-95 degree weather. My problem is dealing with heat soak. My car is typically 140 degrees inside, and it take 15 minutes for the vent temps to drop into the 40's. I typically have a 20 minute drive home, so I am hot for most of the way. Once the system catches up, it seems to work just fine.
I will recheck my T & P's once the weather warms up, and report all, with and without fans.
Take care,
Dave

Hi Dave, just dropped by for a moment,

you need your vent temps @ about 35-37/38 F quicker in say a block or 2 or maybe A Mile "as fast as possible" and sustained; just above evaporator freezing point to bring the cabin air temp down much faster, 15 minutes is not good, as I am sure you know @ 90-95F your sweating

this might not be possible with your pfc eficency you have

adding additional fans to your rear condenser is ridiculous and a waste of money (sorry don''t know a better word for this, its not personal) if your rear PFC is SEALED properly to the deck lid letting your engine large fan do the work

However INCREASING the air flow into and through your front condenser with a better blower will help you both at idle, stop and go driving, as well as extended driving

[DaveMcKenz]

Thanks Reid,
I am just trying to do the best I can with the system I have. I do have an upgraded blower on the front condenser. I have also sealed the rear condenser to the deck lid. I had the 8" fans left over from a project on my 928, so I thought I would try them to supplement the rear condenser air flow at low engine RPM's. It will be easy to run with and without the fans later this Summer and get some actual data on vent temps and a/c pressures. I will report soon.
Thans for the suggestions.
Dave

[KelogGes]

I know you are trying to do the best you can with what you have !
have you ever read through my original thread, there is a wealth of info scattered you have to dig though the crap to find, there is a lot of useful a/c tips and tricks there I have written!

Just so I know are you using a thermometer to measure your vent temps? preferably a digital one
IR is surface not air and there is a difference

[Bob Kontak]

Originally Posted by wwest

I suspect Bob mean to say:

"If you have a pre-84 911 with manual.."

otherwise the article makes no sense.

Link in post 47 does not specify year when it discusses manual controls.

I must not have understood it. Figured it was a follow on to the post 83 discussion. You have manual controls or you have spiffy controls in the post 83.

[DaveMcKenz]

Thanks, Reid. I did indeed read your original thread of 2-3 years ago. I have several different thermometers, digital and analog, also IR. I will publish rear condenser inlet/outlet temps with and without electric fans, once the weather gets hotter. I am working with small, incremental changes, not total redesign, as is your case. We shall see.
Dave