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Discussion Starter #1
I reported yesterday that the high pressure hose blew on my 66 coupe while charging the system. To recap, I installed a new condenser and dryer as well as the aluminum low pressure line that connects to the bottom of the dryer. AC has never worked, in fact was sitting in a box in the trunk until recently.

When I charged the system the gauge on the low side read 45 - 60 psi high at first, then dropped down to near zero rather quickly. I could not use my high pressure gauge because the retrofit I bought did not include a fitting that would fit the Schraeder valve on my compressor -- so I was charging half blind.

After a can of a half of 134A was added, I checked for leaks with my electronic leak detector. Found a leak on the line at the back of the evaporator. Snugged it down and the leak appeared to be 99% gone.

By the way, during the charge so far, no cooling effect was noted.

After stopping the leak (which I assumed was causing the pressure drop) I started addig another can. Because the pressure was at zero, I assumed I had lost most if not all of the refrigerant I had added. Thus, I thought I was undercharged if anything.

As I started charging, there was a loud boom -- the high pressure line had blown.

Someone on line has suggested a blockage in the system somewhere, my question to the group is: what's the best way to isolate the blockage?

Another question: should I be able to blow compressed air freely through the evaporator? I tried this to get the old oil out of that section of the system and air did NOT flow.

Could a stuck expansion valve cause this? Is there a way to test this theory without taking out the underdash unit? I'd hate to yank the console out -- just restored it and it's a pain to get screw holes lined up...
I'm going to buy either a set of professional manifold gauges and hoses or the proper high pressure retro fitting for my compressor so I can monitor both hi and low pressure readings, but can anyone suggest something else to try?

If the expansion valve is shot, can I replace just that part? Is that something NPD would carry?

As always, thanks in advance for your time in answering these questions.
 

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First - You can rent gauges at AutoZone for a reimbursable charge. Your intital problem may well have been caused by too much pressure in the line because the line was not vacuumed. After you fix your leaks, you need to evacuate the line to about -28 in order to make room for your refrigerant and have a much more effective running system. Luckily, when you rent your gauges you can rent a vacuum pump at AutoZone. Together this will run you about $325, but you will get it all back when you return them.

Since you have to vacuum the system anyway, you really need to flush the whole system. Do not flush through the components (you can flush thru the condensor), only the hoses. You should replace the dryer/evaporator and expansion valve as these are the most likely sites of the blockage and they aren't all that expensive. When you say you installed a new evaporator was it new or just new to you. If it's new, I can't see any reason why it would be at fault.

Also, I just recently went through an a/c fix nightmare, but am happy to report that i was able to get the a/c working on Saturday. A big help were the folks at this auto a/c forum:
A/C Forum

The only other advice I have is, when something it's going right stop and think about (like overnight) it before going forward. I ended up at the junkyard and A-Z several times to replace things I broke because by the time I figured out the logical answer, it was too late.

Good luck.
 

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Thanks. I got on another ac forum and one of the moderators was very helpful. His best guess is that my expansion valve is stuck open causing the blockage. I had noticed during my attempt to flush the evaporator that I could not get compressed air to blow through the unit.

The moderator pointed out that the high pressure I was reading on the low side that drifted down to 0 was initially caused by the pressure in the can of refrigerant. As the compressor sucked the refrigerant out and into the high side the pressure dropped to zero since the can was empty. With the expansion valve closed the refrigerant had no place to go, and since I foolishly kept adding refrigerant thinking I was losing it though a leak, the high side pressure apparently way too high.

The reason I was getting no cooling (again, according to the moderator) is that the refrigerant could not get past the expansion valve.

Sounds right on the money, hope he's right...

I've ordered a new hose and expansion valve from NPD which is close enough to drive to. Plan to try this again tomorrow. Keep your fingers crossed for me, ehh.
 
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