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740 Service R12 or convert to R134-a

ac

I would replace the orfice tube if it has one. Then pump it down. The port should be on the back of the compressor. I have a 93 240 I can go check it if needed. You can barrow a vacuum pump from autozone. When filling with freon, make sure you bleed your gauge or you will get air in the system (not good.)

You really need to get high side guage on there. Ive seen where the low side looked fine but the high side was sky high. If you need help you can call me and I will walk you thru it. But you need some gauges (autozone loaners if needed) and a vacuum pump. And some patients.
 
You only need one side to recover and recharge. Being able to read the high is nice, but not completely required.

I just fixed the AC in my 1990 240 with just the low side, but as u told you, I use a machine to weigh the proper amount of Freon.

Just slapping a can of auto parts store stuff in there isn't the correct method.

Some shops only charge you for the refrigerant. I would have it recovered. Do a new drier and seals on those hoses, find a way to vac it down, then add the proper WEIGHT of refrigerant and measure the vent temps and feel for a hot outlet and cold inlet of the compressor hoses.

Low side will stay high if the compressor is shot.
 
I would replace the orfice tube if it has one. Then pump it down. The port should be on the back of the compressor. I have a 93 240 I can go check it if needed. You can barrow a vacuum pump from autozone. When filling with freon, make sure you bleed your gauge or you will get air in the system (not good.)

You really need to get high side guage on there. Ive seen where the low side looked fine but the high side was sky high. If you need help you can call me and I will walk you thru it. But you need some gauges (autozone loaners if needed) and a vacuum pump. And some patients.
I have a set of manifold gauges but I will need to rent a vacuum pump. Do I need to completely evacuate the system before pulling a vacuum? Also, do I need to replace the drier and the orifice tube before or after pulling a vacuum? Also your 240 uses 134 so it may be different.
You only need one side to recover and recharge. Being able to read the high is nice, but not completely required.

I just fixed the AC in my 1990 240 with just the low side, but as u told you, I use a machine to weigh the proper amount of Freon.

Just slapping a can of auto parts store stuff in there isn't the correct method.

Some shops only charge you for the refrigerant. I would have it recovered. Do a new drier and seals on those hoses, find a way to vac it down, then add the proper WEIGHT of refrigerant and measure the vent temps and feel for a hot outlet and cold inlet of the compressor hoses.

Low side will stay high if the compressor is shot.
Okay so I can pull a vacuum just off of the low side and it?ll be fine. Should I replace orifice and drier before pulling a vacuum? I know I need to ?evacuate? the system before replacing parts. Last I checked, a vacuum pump can both evacuate the system and pull a vacuum. I had thought you needed a special machine to evac the system.

I was going to just take it to a shop until I realized how expensive AC work is.

I think the 740s system is holding pressure so I do not believe there is a leak. Something weird is definitely going on though.
 
So to evacuate and vacuum the system I need a vacuum pump. Can I vacuum and evacuate from the low pressure side only since i cannot access the high pressure side? After that I want to fill with duracool and see what it does.

Another question: when I bypassed the low pressure switch on the drier, compressor ran constantly. When I plugged it in it cycled rapidly. How do I know if this switch is bad, and what tells the compressor when to cycle on and off? Surely it’s not the ecu in a car this old.
 
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So to evacuate and vacuum the system I need a vacuum pump. Can I vacuum and evacuate from the low pressure side only since i cannot access the high pressure side? After that I want to fill with duracool and see what it does.

Another question: when I bypassed the low pressure switch on the drier, compressor ran constantly. When I plugged it in it cycled rapidly. How do I know if this switch is bad, and what tells the compressor when to cycle on and off? Surely it’s not the ecu in a car this old.

The low pressure switch is simply an on/off switch. The fact the compressor came on at all when the switch was in the circuit tells you it is working as it should. Yes, simply vacuum the system down using the low side port. That will evacuate the entire system. Once you do that, charge it by weight. You an get close enough since you know how much each can of refrigerant holds. Weigh a full can and you will know exactly how much you have put in the system if you keep track of the weight of the last can needed to fill the system. Math is your friend, utilized it.

I took a look when I was at my shop yesterday. Some of the R-12 7/9 series compressors have a high side port on the back of the compressor, some don't. Volvo used 2-3 different manufacturers for their compressors.
 
The low pressure switch is simply an on/off switch. The fact the compressor came on at all when the switch was in the circuit tells you it is working as it should. Yes, simply vacuum the system down using the low side port. That will evacuate the entire system. Once you do that, charge it by weight. You an get close enough since you know how much each can of refrigerant holds. Weigh a full can and you will know exactly how much you have put in the system if you keep track of the weight of the last can needed to fill the system. Math is your friend, utilized it.

I took a look when I was at my shop yesterday. Some of the R-12 7/9 series compressors have a high side port on the back of the compressor, some don't. Volvo used 2-3 different manufacturers for their compressors.

Awesome, thanks. There looks to to be a threaded nipple on the back of the compressor, maybe even 2. Any way to tell which one is for the high pressure side? I assume it’ll be on/near the smaller high pressure line. Plan today is to vacuum down the system with a rented AutoZone vacuum pump. Hopefully I can boil out all the moisture and hold vacuum for 30 minutes.
 
The nipples line up with the hard lines. A 240 compressor has both high and low pressure ports on the back. You can have a compressor with both, with only a high side port, or, none at all.
 
Getting ready to order some parts.

What brand receiver drier do I need? They range anywhere from $12-$32.
Something like this four seasons brand work? Found it for like $16 on Rock Auto.

Then I was assuming it would be a good idea to also purchase an orifice tube which if I'm not mistaken is the same as an expansion valve. Anything else I'll need besides duracool, a vacuum pump and manifold gauges?
 
A car has either and orifice or thermal expansion valve. Never both.

Get new seals, orifice, and drier.
 
Turns out my compressor on my 91 took a dump, suction-side pressures through the roof and it won't cycle...joy. Glad to see you're making headway, Promise.
 
Turns out my compressor on my 91 took a dump, suction-side pressures through the roof and it won't cycle...joy. Glad to see you're making headway, Promise.

No headway yet:lol: waiting for parts to arrive and who knows if my compressor is bunk.

Also I have been doing some research and emailed the ES12A company. I am going to get that rather than the duracool because it’s cheaper by a LOT. Also, you can (and are supposed to) charge the system at atmospheric pressure, NOT under vacuum. I was told that even after vacuuming the system, I won’t remove all that much oil. I will add maybe 2oz of ester oil while refills with ES12A.

Is there any way if me telling if my compressor is bad before dropping all this money into the system?
 
Not overly sure on the 740 system, but on the 240, it has the pressure switch at the receiver drier. When you jump the two wires it will engage the clutch on the compressor and run(if it works).
 
Not overly sure on the 740 system, but on the 240, it has the pressure switch at the receiver drier. When you jump the two wires it will engage the clutch on the compressor and run(if it works).

Yeah it runs fine but I don?t think that means it?s actually compressing. I jumped it and let the compressor run for up to 30 seconds straight and it created no pressure or heat in the condenser at all. I?m hoping it is just over or overfilled and that?s why.
 
What is your pressure static(engine off for 5-10 minutes)? What is your pressure with the engine running, compressor off? What is your pressure with the engine running, compressor on?

If your static pressure is low, you most likely have a low charge. If you see no pressure change or a high pressure with the engine running it's most likely a failed compressor.
 
Today I replaced the receiver drier and vacuumed the system, then filled with ES12A. Air is pretty cool (not cold) after adding 2 cans. But now the compressor is on constantly when the ac is on. Any idea why?
 
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