My 72 El Camino compressor bearing failed, I lacked the cash for the repair so I removed the compressor and hoses and stuck them in a box. That was 30 years ago. This summer I decided it was time to fix it. I am not an A/C guy;

  I purchased a new condenser and dryer from Ground up, nice stuff fit nicely, new compressor, expansion valve, oil and 134a came from O’Reilly’s. Installed new parts, 134a ester oil and replaced all o rings with green ones. Pumped the system down to -29 inch’s (above sea level here) and let it sit over night. Next day, no leaks, so I serviced the system with 20oz of 134a started the truck added 22 more ounces of 134a and had 40* air coming out the vents. This lasted about 20 minutes then the temp started creeping north to 50* more on this part latter.

  It lacked flow out the vents so I started trouble shooting the valves/doors in the system for proper operation. I used a shop vac for system vacuum; put the vacuum in the next room so I could hear the valves working. I removed the valve and door from the upper cowling, inside passengers kick panel and distribution box from the front of the heater discharge to see all valves then ran the fan on all four speeds normal and max.

  Everything seemed to work till the fan fuse blew. I removed the inner fender and replaced the blower motor. It increased the flow some but not to where I thought it should be. Kind of running out of ideas I started putting things back together. During the trouble shooting I had removed the hose from the upper cowl valve and plugged it with a golf tee when I went to install the valve I noticed the tee missing.

  So I start looking for the tee, take the fan back out to make sure it’s not in there, start reaching into spaces no man has ever been. Reaching through to fan hole and back past the fire wall I find the tee. I also find 38 years of leaves, dirt and nests. The back side of the firewall from the fan down to the recirculation valve was packed solid. Even thought the valve was still working no air could pass through it. I removed the recirculation valve and filled a shopping bag with the stuff that came out.

  I then checked the evaporator box by looking in through the resister mount opening with a bright light, it was full of leaves. Using two feet of heater hose hooked to the shop vac hose and a piece of coat hanger with the fan running I removed all the leaves through the resister opening in about an hour.


  Now I have great air flow. I can get back to discharge temps. Once the systems warms up the temp go to about 50* Some guys like numbers so here they are.

  1000 rpm high side 180psi, low side -40, OAT 80* duct discharge temp 48*

  Next day I take it for a test drive, 30 minutes of stop and go driving OAT 80* duct discharge temp drops to 28* yea 28* and stays there. Pull back in the driveway and the temp suddenly rises to 48*. The system does not seem to be able to stabilize. It either gets to cold or to warm. POV valve is 38 years old and not calibrated for 134, so it may need to be replaced.

  Questions: There is a thermal switch on the side of the evaporator box. What temp does it open at?   Does it disengage the compressor?   Is it to prevent icing?


In spite of everything I’ve done the system is still trying to work. Just trying to get it to stabilize.
　

I researched converting my '72 to 134 a few years ago, but never got around to it.  I do remember that in '72 only they had what was called a superheat switch on the back of the compressor, and a resistor mounted on the evaporator box.  I'm not sure of the exact function, but it might be the termal switch your seeing.  Also, the POV need to be adjusted for 134.  You hook up an air compressor and adjust a screw inside.

I got most of my info here: http://www.autoacforum.com   Lots of info and people willing to help.

Here's instructions on adjusting the POV  http://www.autoacforum.com/messageview.cfm?catid=20&threadid=16311  

Thanks Steve good info and sites. My research tells me that a 72 was deferent from 70, 71 and 73. There is a thermal overheat fuse that is in the compressor wiring harness right near the compressor. On the evaporator box there are three elect parts, (1) Relay to control fan speeds (top inboard), (2) a resister that controls fan speeds 1-3, (front lower) power bypasses this for high speed and sends 12 volts directly to the fan motor. (3) a temp bulb (outboard lower) that I think is designed to disengage the compressor if the system gets to cold. As good as it feels 28* is to cold things start to ice up and condensation forms on the ducting inside the car. The Elky used the same system that was used in the coupes, verts and wagons, so when the system is working it can freeze you out. So either the POA valve (still needs to be set for 134) is sticking, or the temp bulb is not disengaging the compressor, or both. I should be able to trouble shoot the temp bulb by unplugging it with the compressor engaged. Anyone have an idea what the temp bulb is designed to open at?

I didn't see this post before I started another in General, but I have a POA valve you can send in for rebuild/adjustment.

Ok I'll post here to; are you in town this weekend?

dashboard wrote:

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  1000 rpm high side 180psi, low side -40, OAT 80* duct discharge temp 48* 

  Questions: There is a thermal switch on the side of the evaporator box. What temp does it open at?   Does it disengage the compressor?   Is it to prevent icing? 　

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If your saying negative 40 on the low side. Thats no where near enough pressure.

Also, its likely that switch is actually a pressure switch instead of thermally activated. Which sheds some light on the low side pressure reading.  

  My typo, should read +40. System should be +26.5.  Mitch hooked me up with a extra POA valve yesterday.  I'll send it off this week to have it rebulit and caled for 134a.  Seems the more I drive and use the system the better or at least more stable it gets.

Just think it should get colder than 48*

Anyone out there with a 66-72 factory system able to share numbers?

Remember, R12 actually will blow colder then 134A. Especially when its a retrofit. Plus, your not supposed to charge up a retrofitted R12 system with the same amount of 134. About 80 percent of the system capacity.