Hello everyone! I have a 1979 corvette which was converted to R-134a by the previous owner and at the moment does not blow any cold air. At first, I topped off the freon thinking that it could be low, but it is never that simple. I did a ton of research and testing and came to the conclusion that my high-pressure switch was faulty as it did not have continuity and there was no voltage going through. I then checked the compressor and confirmed that the clutch still worked which was relieving in the moment. With that testing, I decided to replace my high-pressure switch as it seemed at the time that it was faulty. Yesterday I had charged the system up to figure out my operating pressures to find the right switch and low and behold, my clutch on my compressor started to work again. However, the clutch would engage (Be still) when the AC slider was set to the OFF position and would disengage (Freely spin) when the AC slider was set to NORMAL or MAX. This confused me as it was opposite of what it should be to my knowledge. I then decided to see if the compressor would blow cold air while the slider was set to OFF as this would engage the clutch. This however did not produce any cold air coming out of the vents. Throughout testing the clutch, I was also monitoring my pressures which seemed to show Higher than normal pressures on the low side and lower than normal pressures on the high side. I am not really sure where to go from here and any information would be appreciated! At the moment my thought process is that my pressure was too low for my pressure switch to be on so the clutch would not engage. However, after charging the system, it engaged as the pressure was high enough. Everything else though I am not sure about. For reference, the ambient temperature outside was about 89 Degrees Fahrenheit while having roughly 55 PSI on the Low side and 100 on the High Side (These are measurements after I took the manifold gauges off the car, I believe it was around 60 PSI on the low side and close to 150 PSI on the high side while it was on the car).

P.S. I have also read a ton of the forms on here to troubleshoot my AC and have already adjusted the plunger behind the glove box to be on the maximum cold setting.

 

I thought 134 ran@45 low and@220 high?
weird clutch engage.
off closes vents.

 

did you check the orifice screen when you emptied and recharged?

 

Don't know about the reverse operation of the compressor, but based on the pressure readings, I think your compressor is done. ( low side high and high side low) As for the Comp. Cycling Sw. it should cutout at around 30psi and cut-in around 50psi these are low side pressure ranges. Also know that it is very easy to over-charge a R-134a system, once over-charged the performance of the system drastically deteriorates. Too much is worst than not enough.

 

When you removed the high pressure switch you opened the system to air. The system has to be evacuated before you can recharge it.

 

​​​​​​​Perhaps but I am not certain. I am relatively new to all of this so I am learning as I go. But from what I have read it seems that the compressor is most likely dead like you are saying.

 

Yes, I had the system evacuated before and after removing the switch to ensure that there was only R-134a in the system.

 

OK, that's good. So with air temperature of 89 I would expect a high side of 230 not 150. Are you sure you put enough R134 in?

 

I may not have as I would slowly add some then close the freon can as I did not want the Low side to have too much pressure. I would get it to around 100 PSI then let it equalize to around 30 then add more.

 

You didn't do a conversion calculation from R12 number of pounds to R134?

 

No, I was not aware that I would need to do that. Could you explain that some more?

 

you only use 3/4 of the R12 pounds when switching to R134. So if R12 was 8 lbs you use 6 lbs R134.

 

Ah okay I understand, I didn't even use an entire can which only had .7 lbs. of R134 in it. I may need to add more than to get proper results.

 

The system takes 3 lbs of R12 so you need 2.25 lbs.

 

Oh that's very useful information! Ill add some more in later today and hopefully that does the trick. For adding the R134 to the system, Is the method of adding till like 100PSI on the low side then letting it drop down to like 40 then add more or should I just add until I get the correct high side PSI? I'm assuming adding it slowly is better just so that it has time to circulate in the system.

 

rule of thumb for high side is double air temperature + 50. So put a full 2 lbs in and watch high pressure.