Yet another question for the brain trust.

[asphaltgambler]

I think that most here are over thinking a solution with-out finding more about the cause.

1) Identify whether the car was converted to R134 when the previous major A/C work was done. If it has therin lies part of the source of the issue; deviation from stock designed components. R134 is less efficient and runs significantly higher high side pressures than R12. If indeed it has been and all below items addressed a higher effficiency condenser may be needed.

2) Dirty / clogged condenser fins. You would be so suprised if you removed the grill for access to the condenser, then liberally applied a good cleaner like simple green then power wash and watch the debris hit the ground. What a huge difference it makes in the high side pressure

3) Clutch fan worn out. No airflow for sure will make this happen everytime. From your description of the cars condition and mileage sounds as replacement is no brainer.

4) System is slightly over charged. Pressure = heat. Depending on the vehicle it could be just slightly overcharged but the difference in cooling would be substantial to point of activating the high pressure cut-out switch (if equipped) to cut the compressor when pressures get too high.

[red-beard]

If it was the fan clutch, wouldn't he also see the temp rise on the cooling water system? Several of my older cars had the hydraulic fan clutch and they definitely go bad.

[GH85Carrera]

The center dashboard vent temps with the system on MAX high fan is 40 degree air and a lot of it. It gets uncomfortably cold after 10 minutes blowing on my face. I would not want it any colder. I need to dig out my IR thermometer and read the evaporator temp. The entire accumulator will get cold enough to be covered in condensation while it is sitting in the engine compartment in 15 minutes of drive time. It blew ice cold air last weekend on a 100 mile trip down the highway at 75 MPH. Without my new fan while sitting at a long red light the vent temps go up rapidly.

The fan clutch will go into lockup if I wait at the light for long. I was careful with the oil and the pressures when I replaced the last compressor. The systems is great except at idle. It really has been that way for 22 years.

I remember the day I bought it I took it for a test drive. I loved the AC since at that time I had a non AC 914. I left it running and popped the hood to watch it idle and see what it would do. The engine got warm since it had the stock 2 core radiator. The AC was blowing much warmer. A quick drive down the street and it was back to cold. The only instruments at the time was the speedo and fuel gauge. I replaced that with the factory gauge package back in the 90s sometime.

I have replaced the fan clutch at least twice over the years. There is not much on the vehicle I have not worked on over the years.

I will talk to the AC shop and see what they have for a T connection for the liquid line. I will have to get motivated to want to R&R the system to get the pressure switch in place. That might wait until the next time the compressor dies.

[mattdavis11]

Originally Posted by red-beard

If it was the fan clutch, wouldn't he also see the temp rise on the cooling water system? Several of my older cars had the hydraulic fan clutch and they definitely go bad.

If he had a stock radiator, but he has a larger radiator, a 3 or 4 row core I presume.

If the inside temp rises that fast, you have a vacuum leak, or the heater valve and or blend doors don't work properly. Both are vacuum operated. Sounds to me like the heater core is fighting the evaporator, raising the low side pressure.

Normally, if you can't bring down the low, the high won't come down as well. However, you can bring down the high with a fan to make the evap happier on the low. Using a water hose on the condenser, or a fan in your case, can help the system find an equilibrium where it's happy. This is what you are doing now.

Focus on the low side now.

[GH85Carrera]

The engine was replaced 20,000 miles ago. All new rubber hoses and vacuum connections. There is no sign of a vacuum leak. I had periods in the past of vacuum leaks. I know the signs.

I went and bought a new fan clutch today. The old one has been on there a long time. I will see if it helps. If I hear it lock up more I will know the old one was work out than I thought.

I think the low pressure switch turns the compressor off at 35 PSI but it might be 30. It sure works now.

[mattdavis11]

Grab the fan and have someone fire up the motor. If you can hold on to the fan, bounce the blades around, then clutch is no good.

The LPCO should not have a cut out that high, maybe 10-15.

Replacing the motor doesn't much matter when the problem lies within the cabin.

I'd look to see if you are losing vacuum at the back of the control head.

[GH85Carrera]

I went ahead and replaced the fan clutch yesterday. It is a real simple task, and pretty cheap. It has not been hot yet so I don't know if that made any difference at all.

The system is still R-12 and is the typical GM CCOT style system. The low pressure switch is attached to the accumulator and I will have to check the specs but as I remember it cuts off the compressor in the 30 to 35 PSI.

I did get the second relay installed yesterday. Now the fan will ONLY come on when the compressor is running and the brakes are on. I still need to find a relay with a 10 second delay. Swapping the relay should be a piece of cake. With the delay relay it will keep the fan from running every time I hit the brakes to slow for a corner or traffic.

No doubt the best option will be to graft in a pressure-temperature switch in the liquid line from the condenser. Obviously that requires opening the system. My dual relay jury rig should achieve my goal of running the fan while at a light, but not while motoring down the road. I am sure my alternator will appreciate the lightened load.

[GH85Carrera]

For the few if any folks that are curious how things turned out on this project:

I finally found an affordable (17 bucks) weatherproof automotive 10 second delay relay. I could find lots of expensive ones that were close to or more than $80.

Now while driving along the fan never comes on. If I use the brakes to slow down to change lanes the fan does not come on. Only after 10 seconds of braking when the compressor is running does the cooling fan run.

We did had have a nice hot 95 degree day the other day. I took the wife to dinner and the traffic was heavy. Lots of sitting at long lights. The AC was blowing cold and the engine temp even stayed lower that before.

Overall I am real happy with the results.

Thanks all that made suggestions and especially to Matt Davis.

[onewhippedpuppy]

Well done Glen. Very creative solution to the problem.