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My issue with your your system is that why when you’re driving the vent temp is 60F, same as my 560sl in my garage with 90+ ambient temp. but when stopped and idling the temperature rises to 80F The difference is air flow through the condenser not the evaporator. The evaporator air flow is based on the blower speed.
you should add the correct amount of Pag oil prior to charging Refrigerant. As a certified Refer Tech it sounds like
1- you are over charged, so too much liquid Refrigerant in the Condenser or too much oil. low side should’ve closer to 40-45 psi and steady fluctuations are a sign of weak compressor or over charging.
2-Weak Compressor at your current low side pressure I would expect High side to be 200+ My 560SL idle at 41 Low 250 High with 100f garage temp. 59F vent temp. Minor bubbles in sight glass, glass is clear. The Compressor must be able to push the refrigerant through the condenser at a pressure enough to make it a hot vapor, not a Liquid. Air passing through the condenser cools it to a cooler semi- Liquid
FIX; Reduce Refrigerant to give the compressor a break, and see if that increases you vent temp at idle.
Also the fluctuation of sight glass bubbles is the Expansion Valve opening and closing due to the Heat load in the Cabin. Increasing blow speed may alter the Bubble occurrence.
I hope this helps.
 

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1989 300SE 232k miles
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Discussion Starter #42 (Edited)
Thanks. Your numbers are super helpful. The ambient temperature in the warehouse is about 80 - 90 F.

I’ll set the Freon to 40 - 45 psi tomorrow. And see what numbers I get. And I’ll watch to see if the compressor turns off. Which, I don’t believe it is.

Learning that sight glass cycle is the expansion valve is huge! A great relief.

Thanks!
 

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Discussion Starter #43
The way to remove excess oil is by doing a flush, correct?
 

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It sounds to me like you have a bad expansion valve and probably a compressor on the way out. Your best approach would be to replace the expansion valve and totally flush the system. That way you can add the proper amount of oil and have the system charged by weight of refrigerant not just by pressures. Flushing a 126 car is a real PITA and messy job if done from inside the car. I took an old expansion valve and cut it in half and took the guts out so I could install it and flush the system from under the hood instead. It requires some extra labor but is well worth the time in my opinion.
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20200528_091225[1].jpg 20200528_091252[1].jpg
 

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1989 300SE 232k miles
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Discussion Starter #48
Honestly, I looked at my drier, condenser, and hoses. Other than the new r134a connectors and their immediate hoses, everything else looks old. Like real old. Particularly the ends where the hoses connect to everything else.

It wouldn’t surprise me if the “upgrade” was swapping out those sections of hoses and filling everything with r134a.
 

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Mercedes recommends replacing the drier whenever the system is opened up and it's a good practice to follow. The hoses do develop leaks sometimes usually where the fittings are attached, but the old looking appearance shouldn't cause a problem.
 

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Discussion Starter #50
My issue with your your system is that why when you’re driving the vent temp is 60F, same as my 560sl in my garage with 90+ ambient temp. but when stopped and idling the temperature rises to 80F The difference is air flow through the condenser not the evaporator. The evaporator air flow is based on the blower speed.
you should add the correct amount of Pag oil prior to charging Refrigerant. As a certified Refer Tech it sounds like
1- you are over charged, so too much liquid Refrigerant in the Condenser or too much oil. low side should’ve closer to 40-45 psi and steady fluctuations are a sign of weak compressor or over charging.
2-Weak Compressor at your current low side pressure I would expect High side to be 200+ My 560SL idle at 41 Low 250 High with 100f garage temp. 59F vent temp. Minor bubbles in sight glass, glass is clear. The Compressor must be able to push the refrigerant through the condenser at a pressure enough to make it a hot vapor, not a Liquid. Air passing through the condenser cools it to a cooler semi- Liquid
FIX; Reduce Refrigerant to give the compressor a break, and see if that increases you vent temp at idle.
Also the fluctuation of sight glass bubbles is the Expansion Valve opening and closing due to the Heat load in the Cabin. Increasing blow speed may alter the Bubble occurrence.
I hope this helps.
I misread this before, and interpreted it as a possible condenser issue. Upon re-reading, I believe you meant the condenser isn’t working properly because there isn’t enough pressure from a bad compressor. Is that correct?
 

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Discussion Starter #51
I got my step-father a fiber optic camera for Father’s Day. And it’s first real use was to go inside my heater box and look at my evaporator.

I didn’t snap a picture of when I had a view of the entire area. Nor did I get the one looking up through the cowl. But here’s the entry into the box through the blower fan opening.
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And 2 pictures of the evaporator.
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I’m thinking it’s pretty clean. I’m eliminating clogged outside of the evaporator from my list of causes of my AC issue.

If your opinion differs, let me know. As I’m not an AC guy. ...I just really wanted to show pictures from the fiber optics camera 😉
 

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1991 500SEC 55K mi. 1987 560SEC Now 153K mi. 2020
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Great pics!

Before you button it up, you might do another take, this time shooting straight down the evaporator face after you have the probe well in there.

It's down there, not in the 'direct' airstream that I found a LOT of stuff.

Cheers,

M
 

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Discussion Starter #53
Great pics!

Before you button it up, you might do another take, this time shooting straight down the evaporator face after you have the probe well in there.

It's down there, not in the 'direct' airstream that I found a LOT of stuff.

Cheers,

M
I appreciate that. I did. I looked near everywhere.

This was from yesterday. I was in there a good 10 minutes before I realized I wasn’t saving any pictures. ...the blower entry pic I took on the way out.
 

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Discussion Starter #54
I wish I had a one or two of the “wide angle” views. I saw everything in there.
 

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Discussion Starter #55
Now that I feel ok about the outside of my evaporator, and since I previously flushed my condenser, this morning I decided to look at my pressure gauges. And as I’m doing so, I blew an o-ring. So I looked at my other o-rings and noticed the one on the hose I use to add r134a was bad. That’s why, even though the cans say 5 - 15 minutes, it took so long to fill last time.
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Anyway, today I flushed my evaporator and my expansion valve (I know it’s taboo, but I figure the valve is built to take waaaaay more pressure than I used. And Ferrari guys do it. So... who am I to question guys that work on Ferrari’s?) I wound up with a goodly amount of oil and dye and probably stop-leak.
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After a 2 hour vacuum and holding pressure test, I refilled with r134a. With the appropriate 2 lbs of r134a, I’m at 45 psi Low and 240 psi High. That’s with an ambient temperature of 95 F. The car blew 67 F in the warehouse. When I took it on the road, it blew 48 F, which is the first time it’s done that at prime sun/heat time. Which was exciting.

At the only red light, it crept up to 65 F, but no humidity. And when I went to Neutral and bumped the idle to 2000, it dropped to 58F before I had to move. The engine was at about 90 C.

I’m thinking my fan clutch isn’t working right. That after these two flushes, with proper air flow from a proper fan clutch, my AC may work right. ...Or my compressor could be dying... Or my condenser is bad... Or I blew out my evaporator... And while I have a replacement compressor on its way, rebuilding my fan clutch is my next step.
 

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350SDL, '17 GLS450, "Grandpa's Roadster" Project Car
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while I have a replacement compressor on its way...
If you're getting 45 psi on the low side and 240 psi on the high side at idle I don't think there's anything wrong with the compressor...

If the fan clutch housing is empty then fixing it might help the AC, otherwise, I doubt it will make any difference.

Is the aux fan coming on with the AC?
 

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Discussion Starter #57
Glad to hear you think the compressor is ok.

The aux fan comes on. But it does not come on immediately when I turn on the AC. And I understand this is a 2-speed fan, but, to me, it seems to only have 1 speed, high. ..I ordered a potentiometer. I plan to hook that into the aux fan wiring and get it to turn on at a lower temperature. Particularly since I have a lower temp thermostat.
 

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Discussion Starter #58
Went for an hour drive. 83 F at 7:30p tonight. The car blew as cold as 42 F. And never went over 50 F at a red light.
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It was so cold, in fact, when I turned around, my teeth were chattering. I couldn’t run it at Max cold anymore.

I’m going to work on the fan clutch because I’d prefer the engine run cooler. But otherwise, unless it starts blowing hot or something breaks, I’m happy.

Thanks everyone for all your help!!!
 

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The aux fan comes on. But it does not come on immediately when I turn on the AC.
It's pressure activated, so that makes sense.
And I understand this is a 2-speed fan, but, to me, it seems to only have 1 speed, high.
When the pressure switch activates it closes the low speed relay which powers the fan through a (big honkin') resistor. Unless someone bypassed the resistor, it should not run at full speed until...
I plan to hook that into the aux fan wiring and get it to turn on at a lower temperature.
Logic driven by the coolant temp sensor triggers a different relay that powers the fan directly, bypassing the resister. To test the fan motor, run a jumper wire directly from a source of battery voltage to the fan motor. If it runs at the same speed as when the AC comes on, something is wrong.
 

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Discussion Starter #60
It's pressure activated, so that makes sense.

When the pressure switch activates it closes the low speed relay which powers the fan through a (big honkin') resistor. Unless someone bypassed the resistor, it should not run at full speed until...

Logic driven by the coolant temp sensor triggers a different relay that powers the fan directly, bypassing the resister. To test the fan motor, run a jumper wire directly from a source of battery voltage to the fan motor. If it runs at the same speed as when the AC comes on, something is wrong.
I’ve jumped the aux fan by connecting these two white connections to one another, jumping them with a fuse. When I do that, that’s the speed my fan runs at.
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Is that adequate for how you suggested direct wiring it?
 
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