Reaper19

I am looking for some electrical help. I did a retrofit on my AC from R12 to R134 for my 1981 Vette and it just does not cool. Best temps I get are around ~67 degrees on a good day when not to hot here in sunny Florida. I had the pressures checked twice and they were normal. Previously I upgraded the radiator with a DeWits and the car runs cool ~185 degrees always. The AUX Fan does not come on since the car runs cool and is set from the factory to not turn on until 238 degrees and shut off at 201 degrees.

I went to a couple different AC mechanics and the conclusion was to get more air flowing across the condenser to get the air cooler inside the car. The last one I saw said he has seen the same issue on other classic corvettes after they were converted and required a constant running fan when the AC was turned on to cool down the condenser.

I did some research and put together a drawing of the idea I have for turning on the factory AUX fan when the AC turns on as well as not modifying the ability for the fan to also turn on if ever needed through the engine temperature sensor. My idea is to tap into the power line that goes from the Function Control Switch to the Idle speed Sensor and Pressure Switch to use as my power source to click on a relay. I was looking at using the relay to complete the ground that is also used for the Engine Temperature Switch.

I used a 5 pin relay in the drawing, but I think I could also use a 4 pin? Anyone ever try the same or know if this would work?

Thanks

Street Rat

It should work fine Reaper.

I wired my fan to stay on when the key is on. I can also change back to the temperature switch option when it's cooler out. But here in the Texas summer it needs to be on all of the time it seems.

Two things.
Are you running a good fan clutch?

You need to get a lower temperature sensing switch that cuts the fan on earlier than the factory switch.

Reaper19

Thanks Street Rat. I am usually pretty good when it comes to electronics, I installed my own Viper Alarm system with remote door locks, took two weekends, but this one had me second guessing myself and wanted to make sure I did not blow anything out .

I run a fan clutch, I think it is still original but it works. Any recommendations for a replacement fan clutch? Also, thanks for the lower temperature sensing switch suggestion. I am hoping the get the AC cooling down properly first and then onto the next project. :-) Fun, fun, fun.

Street Rat

The fan clutch I used was from an earlier model. It was a GM 88961768. I also added a seven blade fan as the factory fan was only five blade. The fan blade was a GM 469580. They were both available from GM last year when I purchased them. They fit my '81 without problems.

Another problem is the factory type condenser. You can buy a parallel flow condenser which is a better design. But your a/c is already buttoned up. I'd save that as a last resort. Make sure you have all your hood seals intact also.

Street Rat

Link to thermostatic switch that I use...

https://www.summitracing.com/int/par...illocation=int

Reaper19

Was your originally a 1 post? Mine is a two post in the 81?

Street Rat

My factory sensor was two wire but you can replace it with a one wire sensor. Check where your two wires go. One is probably a lead to an emission device and the other to the fan. What color are the two wires at the connector?

The sensor grounds internally when it reaches it's opening temperature. It then completes the circuit to run the aux fan. So both wires can be connected together. It apparently is wired to operate two devices. Probably one goes to the computer and the other the fan.

Reaper19

The wire coming from the fan going into the first sensor spade is Blue. The second wire coming out of the second sensor connector spade is black. The way they have it running is just a ground connection coming off of the sensor to complete the circuit. What you say makes sense thought, the sensor is grounded to the engine block anyway. Not sure why the factory decided to add the second spade and black ground wire. I know in the later models the second wire is used for a ECM/computer connection. Maybe GM in all of their wisdom was thinking ahead, even though the 81 computer did not make use of it.

SIXFOOTER

That particular sensor is simply a switch that passes current through the 2 contacts instead of as in other sensor switches that go to ground. The black wire is ground and the sensor connects it to the fan when the engine gets to 238* as stated above. No idea why they did that on this one. Your circuit will work in that it will turn on the fan. However I don't think it will bet your vent temps down. When you had the conversion done did they change the orifice tube? Have you done anything else to improve the duct work in the dash? That car is old and the seals on the inner doors are likely gone, your also likely to have a 1" gap between the main duck the the center dash duct. The fresh air door may or not be working, the hot water shutoff for the heater may or may not be working...SO, you got some work to do to get that thing to cool correctly. If you have a way to get a temp probe onto the evaporator it would help to know if the thing is cooling correctly and maybe only a duct issue

Reaper19

Thanks for verifying the circuit and relay will work, much appreciated. Not positive if the orifice tube was changed, the mechanic said he had to buy a kit to do the retrofit. The mechanic that did the machining on the engine when it was rebuilt came to an agreement to do the retrofit for free since he twisted the AC hose and all the R12 leaked out through the seals on the hose when the engine was removed. The system was cleaned, and vacuum tested. He does a lot of engine and machining work as well as AC repairs, so I hope he did it right. The pressures were checked a few times and they are good.

I checked the fresh air door and replaced the seals on the door, they are working as they should and seal great. I changed out the hot water shut off when the engine was rebuilt, adjusted and tested again recently. The previous owner took the evaporator out and replaced the inner and outer seals. The fan was also replaced by the PO and will blow your hair back, especially on MAX.

That is why it is puzzling why it won't get cold and the compressor constantly runs. I went to a few other AC mechanics and they ended up saying the car needs more air flow.

I need to order and install new radiator seals, currently they are not installed. That will be a fun job with the radiator installed . I worked on the AUX fan tonight and while testing the fan when jumping the blue negative wire to ground at the sensor switch or near the motor it would not run, but it would run if connected directly to the battery. I ended up cleaning all contacts back to the fuse box and found the 30 AMP fuse with a layer of corrosion causing an Amperage drop. After cleaning the fuse box and installing a new fuse the fan is working as expected. I can now move onto installing the relay circuit.

Street Rat

Good news.

Keep us updated Reaper19.

Reaper19

Good news and the investigation continues. The PO replaced the blower and did some work on the exchange box and left a small hole that was blocked with a SS screw for testing in the box on the engine bay side to insert a temperature probe/gauge. I picked one up yesterday and tested the temperature from the evaporator box and it cools to ~45 degrees . When checking what is actually coming out of the vents at the same time in the cabin the temperatures are ~76.

So this seems to lead to hot air intrusion into the vents or the exchange door is not closing properly all the way when set to cold. I tested during initial start up with a cold engine and get the same results as a warm engine. This leads me to believe the hot water shut off is working and the issue points in a different area of air exchange. I am going to work on that area of the car next to see if all is functioning or if I can somehow locate why I am losing so much cold air from the evaporator box to the internal cabin and air vents.

At least the troubleshooting is getting me closer. I did pick up a 4 pin relay yesterday, but have not installed it yet to get the AUX fan to turn on with the AC. That will come after I track down the air exchange issue.

Street Rat

Maybe you have already tested this or I'm misunderstanding your post.

There is a flapper door in the right front fender which is supposed to close when your a/c is on MAX A/C. You can see it through the air intake screen in the cowl. The rubber on these deteriorates over time. A vacuum pod controls the door. Just two more items to look at.

This...http://www.parts123.com/corvettecent...50g&ukey=37216

Reaper19

Thanks. I will check again, I replaced the gasket/seal on the lower inside door a few months ago and checked it's functioning, it is working and sealing well and it opens at max as expected. I tried to look at the upper valve and fresh air door you mentioned but could only feel and hear that it is closing. I can also feel the outside air stop flowing through the fender screen when on max. But I am going to do as you suggest and maybe look at it more closely, maybe get a mirror down there to look and if I need be replace that seal.

I'm going to take out the glove box again, unhook the cold/hot selector cable and see if I can feel and hear the blender door close in both directions. Someone mentioned you should be able to hear the door close in either direction. Hopefully either of these two issues, blender door or upper fender fresh air door will correct the cold air loss.

You help is much appreciated

Reaper/Randy

Reaper19

Can anyone take a picture or explain what vacuum lines connect to which of the three ports on the vacuum water shutoff switch behind the glove box?

I spent today going back over all connections, vacuum and wire to make sure all was setup correctly, but I am still getting warmer than expected AC air in the cabin. All vacuum valves for air flow MAX and Normal are functioning perfect. I did find the PO messed with the lever that hits the button on the switch and bent it to the right, then put a block of rubber rigging on the lever. Not sure why he did that? I bent the metal lever connected to the exchange door back to where it should be and adjusted per the AIM manual, along with adjusting the cold/hot selector cable.

After adjustments I am getting the same as before, cabin AC air through vents 78 degrees, evaporator box 58, and temperature outside 96.

Does anyone know which vacuum line goes to which port on the vacuum switch behind the glove box or have a picture of one connected and working? Currently mine are set up as PO had them, Black to port on the right nearest the button, White stripe in the middle, left most port nothing connected.

I read some conflicting information on the web, some owners say there should be vacuum to the water shut off valve when the the selector on the controls are set to cold and some say vacuum is applied when selector is on hot?

I can feel the heater hoses, one is cold and one is hot when selector is on COLD.

Here is a picture of the valve that is identical on Wilcox Corvette site.

http://repairs.willcoxcorvette.com/1...hut-off-valve/

Street Rat

Reaper19 send your email address to me in a PM. I can't send the photos by PM.

Reaper19

Email sent.

Thanks

Street Rat

Sent the diagrams just now.

Craig

Reaper19

Well the black stripe vacuum hose was on the wrong port for sure on the vacuum switch. I changed it to the left/rear port as the AIM drawing shows and the Cold/Hot water shutoff and vacuum switch are now functioning correctly and the hot water valve cuts off the hot water. Unfortunately the AC is a bit colder but not were it should be. I am getting 58-60 degrees in the evaporator plenum and 78-80 at the cabin vents with the outside air temp at 90 degrees. I did notice about a 4 degree lower temperature while driving versus at idle. I do notice when I go from MAX to Normal I need to slightly wiggle the selector switch to make the fan go on high/max, but not when I go from Vent to Normal or MAX.

The only thing I can think of is trying to pick up a can of R134 with a gauge or getting the system checked or the pressures checked again as well as Freon level. Not sure how accurate I can check with one of those cans and gauges from the auto parts store. I called a few AC repair shops and one said 150 bucks to evacuate, pump out the air, clean, refill, put in dye and check for leaks, then see if anything is wrong with any parts of the system. That is their troubleshooting method. One said $19.95 to put gauges on and check the system. A few others said they do not work on classic cars or retrofit from R12 to R134.

Thank you for your help pointing me in the right direction in hooking up the vacuum lines, diagrams and finding everything is hooked up correct now.

Street Rat

Darn. This thing is being a pain.

You need to have someone test the pressures and put in some dye.

Did you replace your accumulator (good source of leaks)?

Did you replace the orifice tube? If not maybe it has debris clogging it.

Simply a few more things to check.

I had mine at the A/C shop five times before I got it right. Leaks and more leaks. So I feel your pain.