I had my 85 IROC converted to 134. The mechanic who did the work, who has completed many of these conversions, and whom I trust (he's done all the work on my car) is scratching his head. After double-checking everything, the AC still isn't cooling as he believes it should. At start-up, it blows 55 degees, but after the engine warms up, the temp will rise to around 68, and in Kansas' 100 degree heat, that's a problem. Any suggestions or advice?

JamesC

 

James,

Study the temperature/pressure curve for R134A. Get the coil face measurements on the evaporator in a 1985 'F' car, and the condenser capacity. Understand the critical nature of these components, then factor in the small orifice in the expansion control. You'll then see why R134A is not optimal as a replacement in these older (small) systems. You could slightly improve the cooling capacity of the system by sizing the expansion orifice tube to something more optimal for R134A, but the coil sizes are what's really hurting you. With a little more engine temperature, the condenser just can't reject the heat necessary to maintain an adequately cold evaporator. Superheat in the system is probably unreasonably high for such a short line set - another symptom of inadeqaute condensing (in this case, due to the lower heat capacity of the refrigerant).

Newer vehicles can "survive" the hotter days at marginally acceptable pressures since the coil face sizes are increased to compensate for the inferior latent heat capacity of the R134A, but the evaporator of an older R12 system in good condition will ALWAYS be colder than R134A at a given condenser (outdoor) temperature - ALWAYS. It's just the nature of the refrigerant.

If you want to test the condener theory, run a garden hose over the condenser and see if the performance doesn't improve. If the problem were in the expansion control, this over-condensing wouldn't make a lot of difference. If the problem is hot gas instead of liquid at the expansion control, the performance will improve significantly. That should tell you something.

 

Hey, Vader,

Many thanks for your reply. Would swapping in a condenser from a newer Camaro or perhaps from an aftermarket company (should there be one) be of any real benefit?

JamesC

 

This post arosed my interest because I'm try to understand my kid's 92 Camaro a/c performance. It seems like, when hot & idling, their is virtually no cold air, but once the car is moving, cold air from the ducts is apparent. I don't know if this suggestion will help me, but in the case of the original post which converted to 134, would getting the engine electrical fans on sooner help his airflow across the condensor? This suggestion might only be applicable if the duct temps he mentioned were at idle conditions.

 

FJK,

Mechanical fan at idle.

JamesC

 

Your case may simply be the idle speed. The OEM PROM is only set to increase idle speed by 50 RPM when the AC compressor is on. Since the target idle speed continues to drop in steps as the CTS (engine temperature) increases, the two may be offsetting. Your target idle at 240° CTS with the AC on may only be 610RPM in drive, whereas the target at 200°F without the AC is already 650RPM. Add 50 RPM for the AC and the difference in compressor speed is significant. There may be enough of a difference that the AC compressor cannot develop adequate hot gas pressure to force condensing to a liquid in the condenser, regardless of air flow.

If I'm reading your info correctly and you have a mechanical clutch fan, you could also try cleaning the bimetal thermostatic spring/valve assembly on the front of the fan clutch hub. Debris and residue (gunk) sticking in the assembly can reduce the oil flow in the clutch and lower fan speed and reaction time.

Underdrive sheaves will only worsen this condition, if the engine is so equipped.

 

Vader..... huh??? and BTW is this mid-west heat playing on you??
Interesting additional informantion you provided.. everything you wanted to know about everything!!
Are you saying in my case, said a different way, I should increase the idle speed? How's this done on said application? Also, would you happen to know fan strategy for the 92 V6. That is, in simple terms, is the single electric fan suppose to turn when the air conditioning is activated? If so, is it ECM strategy or simple sensor strategy? If the heat isn't affecting you, it's affecting me, so simplicity is the order of the day for me.
Thanks, your friend, FJK