AC only works just ok at 40mph and over
 

Hi, 1980 240d 4 speed here.

Just had my a/c system repaired. New compressor, o-rings, Vacuumed out, new oil and refrigerant.

The system works ok (could be better) when I am driving over 40 mph and highway speeds. When I slowdown and enter stop and go traffic, like in todays 90 degree weather, the system blows slightly warm at best.

I notice when the engine temperature increases in stop and go traffic, the a/c stops blowing cold air?
Could it be the condenser fan? I am having a problem figuring this out.
Is there a way to test that front fan?

Thanks.

Has it been converted to r134 refrigerant? If it has you will need to have a parallel flow condenser installed. If it was charge up with r12 then it sounds like it may be slightly low on refrigerant.

Yes, it was charged with R12.

I am starting to think it needs more refrigerant.
Also, I am going to take a look at the condenser cooling fan. The fact that it is better at highway speeds is leading me to believe that maybe that fan is not coming on and the highway air is cooling the condenser.

At the end of my 125 mile drive today, I left the a/c on and opened the hood and the fan wasn't on.

What are the pressure readings? Does it have a sight glass in the drier?

Yes, if the condenser fan isn't working it will cause low speed problems but it wouldn't inhibit good A/C performance on the highway.

If your engine heats up beyond a certain point it will also shut off the AC, how are your coolant temps and radiator fan? Often an engine with a bad fan clutch will stay cool at highway speeds but rapidly heat up in traffic.

You can check the condenser fans themselves by putting a jumper across the high pressure switch that turns them on to low speed. It's also possible the fuse is blown, I believe they have their own fuse. There is also a resistor that is used by the low speed, if it's failed you will only have the high speed that comes on when the engine is overheating.

My 1993 is like a refrigerator both on the highway and at idle. I converted to R290 as I do all my vehicles. R290 has a lower evaporation temperature and moves more heat per unit of mass flow, to the point where "full cold" will make my hands ache holding the steering wheel.

Fan should have been on.

AC pressure is good. And the engine coolant temperature only rises slightly if I am traveling for a long period of time at high speeds or sitting in traffic.

"You can check the condenser fans themselves by putting a jumper across the high pressure switch that turns them on to low speed. It's also possible the fuse is blown, I believe they have their own fuse. There is also a resistor that is used by the low speed, if it's failed you will only have the high speed that comes on when the engine is overheating."

I think I may have a problem with my fans.
Do I jump the high pressure wire leads or the actual switch? Also, when I do this test I take it the a/c should be on high?

I have 2 separate leads that go into a fitting, and also one wire that plugs into a single fitting and then goes into two leads.
Can you tell me which wires I jump?

I have not been able to locate a resistor for the a/c fan on my 1980 240d.
Is it built into the fan itself or is it a separate unit (block) attached somewhere in the engine compartment?

The key should be in ON but the AC setting doesn't matter, the engine doesn't even need to be running. The pressure switch should be near the condenser on the high pressure line, just short the two wires together that are attached to the switch and the fans should spin up on low speed.

It should be the fitting with two spade terminals on it.

The resistor should be in the engine compartment somewhere, as the fan only has two leads. You can directly test the fan at full speed by putting 12v on those leads.

I shorted the wires together from the a/c switch (two terminals pointing up) and with the ignition on. The fan did not come on. I do not have 2 fans, just one.

I ran 12 volts off of the battery to the fan and it came on. I also cleaned the connector (wire harness) going to the fan in hopes that it may have something to do with the condenser fan not coming on. The pressure switch was replaced.

Does anyone know if there is a relay or a resistor associated with this fan? It is a 1980 240d.

My manual doesn't show one.

I have tested the pressure and temperature switches, and they are good.
The fan operates with 12v directly applied.
I have tried four different relays in each of the two-silver ice cube shaped relays located on the driver's side fender under the black box.

The only thing that I think it could be now is the wiring from the relay to the auxiliary fan plastic wire connector.

Maybe there is a pinched wire or a section that is broken.

Anyone else ever have this issue?

Sugar Bear asked for the pressures. Saying that they are good doesn’t give us what we need to offer better help.

The purpose of the electric fan is to prevent excessive high side pressure. I think chasing the electric fan operation is a worthwhile pursuit, but I think there could be something else going on that is leading to your symptoms. Having the pressures gives us more information to help you with.

Are you SURE Actual R12 refrigerant is used?

R12a etc is not the same...

R290 works well, but really should be a blend of propane and butane...

How clean is the condenser coil?

To know if refrigerant is correct, it needs to either be WEIGHED in, or it needs to be charged with a huge fan blowing across the vehicle with the system on high cool full blower on...
And pressures high and low, with high and low line temps...

It is a process.

Ever get this sorted? This part sounds suspicious. If you don’t have circulation through the condenser you’re not going to get much cold.

My SD is having some auxiliary fan issues. Or perhaps I need to check my fan clutch. During these hot days in SoCal the car is taking a long time to make cold air. It really gets cold on the highway. Two things are possible here - fans or rpm. On 134a (what I use) I may need a little more rpm to get the compressor working. It wasn’t a problem when I serviced the system.

Or it could be the car was just blistering hot after being parked in the sun.

I haven’t heard my auxiliary fan in awhile. I haven’t missed it because it makes an obnoxious whine when I pull into my garage on hot days.

Carl, for what’s it worth, the switch Rollguy sells to keep the aux fan running full time made a huge difference in my 240.

Since my fan clutch is shot on my 91, I keep aux fans running all the time in the summer (by simply bypassing the pressure switch). Engine temp remains stable and AC seems better than ever!

Original poster here.

My pressure and temperature switch have been tested and are working fine. My auxiliary fan is operating when I attach 12v to it, and both relays have been tested (and swapped out with 4 different relays each). The system has a new compressor and has been vacuumed. It has had the proper oil and refrigerant added by a professional a/c tech who works on these vintage a/c systems. The air will blow cold if I am driving highway speeds. When I slow down and sit in traffic in the 90+ heat we have been having, the system and condenser heat up and cannot be cooled because the aux fan is not coming on.

I have determined that there is a problem in my a/c wiring that is not allowing the auxiliary fan to operate as designed. Everything else tests fine.

I have ordered the switch from Rollguy that will bypass some of my a/c wiring and turns the aux fan anytime the compressor comes on.

I'll report back.

That’s all wonderful, but exactly what refrigerant and what are the pressures?

I was wondering the same thing.

Hopefully they went back with r12.

"That’s all wonderful, but exactly what refrigerant and what are the pressures?"

Like I said in post #3; The system has been charged with R12. That's wonderful.

I do not know the pressures; I did not do the charging.
I watched it being done and was told the pressures were correct, but I do not remember the numbers. I guess that is not Wonderful.

We are here to help. We WANT to help, but without knowing the pressures, we don’t have the necessary data to draw a proper conclusion. When you go to the doctor he will listen to your heart and take your blood pressure before he can start a diagnosis. That’s where we’re at with this.

Just trying to help.

I had the same symptoms as the OP. I realized that my aux fan wasn't working at all. You don't have to perform a complex test. When the A/C is on and warmed up, check to see if the noisy fan is on. I had to wire mine to work at all times when the A/C was switched on as opposed to being switched on by the relay that senses the pressure in the system. Also, the parallel flow condenser made a huge difference!

Greg this entirely depends on your climate and usage. On a summer day here in SK the air is fairly cool, but the powerful sun heats the cab terribly. The aux fans are not required at all when cruising on the highway, and in my case they will not come on unless I sit and idle the car with the AC on for quite a long time.

Running condenser fans constantly can result in too much subcooling, frosting up your evaporator or even slugging liquid refrigerant to the compressor in extreme conditions.

I just set up a tractor this week that has a jumper on the condenser fan, however I charged it with this in mind (charge set according to actual subcooling). With a factory system charged by weight, you are changing the parameters by enabling constant condenser fan.

Note that yes it's probably fine in a hot climate like the original poster's and definitely fine for a test. And it's far better than them not running at all due to failed controls. Just something to keep in mind that those fans are switched for a reason.

How can I get one of these and where does it go?

Check out this link, dig around for his contact info. He mailed me mine today and I will report back. Hope this helps.

http://www.peachparts.com/shopforum/diesel-discussion/351863-1985-ca-emission-617-owners-you-need.html

My fan relay mod came in today.
It was quite easy to install. My aux fan now comes on any time the ac compressor is engaged and stays on until the ac is turned off. Not sure if there are any long-term complications not having the fan cycle on and off while the ac is in use, but the good news is, my air is now blowing cold at slow speeds.....and I am happy with that!
Thank you all for your help.

Interesting. I may wire something up to do this. I pulled into my garage yesterday and I heard the telltale whine of the auxiliary fan. I’ll have to check the circuit on the Gen 1 W126 to see exactly what turns it on. My AC was not on when the auxiliary fan was running which I found odd. Clearly I need to look into how it functions.

ETA - I kind of recall doing something like this in my w123. I’ll have to go out to the garage to check it. Perhaps I’ll try to replicate it on the w126.

I got the idea from a video by Jarod on YouTube.

https://youtu.be/-ydCsCSxiiA?si=xcfJd7ljwwl1ADq6

Rich sent me the same kit and I'm happy. My indie said it would cost an arm and a leg to do such but I frequently find other ways around problems.

My compressor.....
 

I replaced my compressor last year after the original one was suspected of being faulty, and the ac has never blown colder (at least in the last 15 years that I owned the car). It's made a big difference.

1991 300d, 256k