AC troubleshooting assistance anyone? (r134) - PeachParts Mercedes-Benz Forum

RavenTBK · #1 08-27-2014, 05:26 PM

I have two concurrent issues to touch on, but first, the specs:

1985 300D
Rollguy 7cyl Sanden retrofit, r134a
16x20 PF condenser
Everything north of the firewall is new, minus the aux fan which still works wonderfully
Evaporator hosed out, and video checked clean

Vent temps are near 55-60*F at their coldest
Ambient temps are 92-98*F

The readings below were taken after 10+ minutes of running at the mentioned speed, to let things stabilize, with a 48" fan on high blowing air through the front end.

At idle speed:
Suction pressure at 45psi
High pressure at 275psi
Vent temp 60*F
Condenser is at high high temperature to the touch, burn yo hand!

At highway speed (2000+rpm):
Suction pressure 30-32psi
High pressure 325psi
Vent temp 80*F+
Condenser cools slightly, its hot, but able to hold it for a few seconds.

First issue is the lowest vent temperature I've seen is 55*F...thats a bit warm compared to what I've seen from other retrofits posted in the forum.

Second issue is the loss of cooling at high speeds. No idea what causes it. I've read from other forums where its a clutch problem, its a low refrigerant problem, its a condenser problem. I have no clue.

My tiny brain suggests expansion valve, as that is the only part that was not replaced...then again, why does it work fine at idle (albeit with comparatively warm temps)? TxV stuck open maybe...but that wouldnt explain the drawdown of the suction side at high revs. It should stay reasonably close to the idle pressures.

Anybody have any good tips?

leathermang · #2 08-27-2014, 06:33 PM

Are you taking those temps at low blower speed ?
With the windows open ?
Tell us more about that fan in front of the car.....

engatwork · #3 08-27-2014, 08:27 PM

How much refrigerant is in it? Numbers sound hi compared to one I recently converted.

vstech · #4 08-27-2014, 10:18 PM

You are overcharged.

leathermang · #5 08-27-2014, 10:59 PM

How did you charge the system ?
Using the site glass ?

RavenTBK · #6 08-27-2014, 11:20 PM

To respond to answers so far...

@leathermang Temps are recorded with the windows closed, doors shut for about 10 minutes to let things stabilize before I pop a door just long enough to feel the vent with my hand, and view the thermo. This is done inside my warehouse, so its shaded, but it is still 95ish degrees inside at the time I did the tests. The blower speed remained on high this afternoon, but even setting a temp and letting the ACC do its thing, it never has gone below 55 since I picked it up from the shop that did the conversion. As for the fan, its your standard mechanic shop style 4foot tall drum fan, placed about 4 feet in front of the condenser, aimed slightly off center to allow the spiral of air to directly impact the condenser rather than ring around it.

@engatwork Couldn't tell you how much is in there. It is whatever the shop's electronic vacu-suck recover and refill gizmo machine put into it. Now, my company mechanic said that 275 was way too high and it was likely overcharged, but according to the temp conversion charts I've found, its dead on the money. Not to mention threads here where folks are pushing 375-400, and replies to those stating from 175 up to 300psi is still golden in 85*F temps. I figure since its so damn hot, the extra 25psi is to be expected. The low side pressures are still right in line with what they're supposed to be, so I dont get it.

Now the small engine shop next to mine has one of those nifty recovery/recycle machines over there. I think I will see about borrowing that instead of just a manifold set, and do a drawdown and recharge to 80% of the r12 capacity and see what happens. I really dont want to take another 125 mile trip back to the shop and end up paying more money if I can help it...

leathermang · #7 08-27-2014, 11:43 PM

Your vent temps may be a few degrees higher than others you have seen posted because you are supposed to have the fan on LOW..
so the air is in contact with the evaporator as long as possible..

FSM says test should be with windows open....

That fan is not sufficient to do this job ..... for filling the system... you would want one of those squirrel cage blowers right at the grill....

Very accurate scales are pretty reasonable now .

The FSM warns that under some conditions you can have bubbles still in the site glass ( which I suggest NEVER be used ) particularly if not enough air is crossing the condensor.

RavenTBK · #8 08-28-2014, 09:08 AM

Alrighty. I managed to get ahold of the next door shops Robinair recycler and fired her up. A full recovery netted only 1.71 pounds of R134. My hood sticker shows 2.9 pounds of R12, while following the 80% rule, should be 2.3 pounds. So, on the surface, it seems as if I was actually low on refrigerant.

Currently shes running a 30 minute vacuum. I will then specify 2 pounds of freon and see what the gauges read, and add small increments as necessary to achieve the desired results.

engatwork · #9 08-28-2014, 09:55 AM

When I did conversion on 85 300cd I ended up with 2.2 pounds in system to make it work.

vstech · #10 08-28-2014, 11:25 AM

the Parallel condenser holds less refrigerant than the original, so 1.7 sounds high to me. I'd start with 1.2lbs, then add in until the suction crests 25 at idle, and see slowly how much it takes to get the suction line temp down to 50

RavenTBK · #11 09-02-2014, 11:03 PM

Now I'm really stumped. 1.2# caused both the lows and highs to be excessive, so I recovered it, went back to 25in vacuum, and began with 0.2#, and crept up in 0.1 increments. I understand I should use the minimum amount of r134 that will yield adequate cooling and still maintain safe pressure.

Basically same shop temps as before, this time with a snail shell squirrel cage fan blasting the condenser.
0.3# is where the suction side crested 25psi
0.4# is where high side climbed to a respectable 175psi
0.5# is where crossover pipe started collecting condensate
0.55# the pressures levelled out to 40/210, vent temp hit 70*F
0.6# reading 42/225, vent temp hit 65*F
0.7# reading 48/235, low side occasionally spiked and compressor belt squeaked ..I assume overfull and trying to pump liquid? I drew 0.1# back out and she quit the noise.

Pretty much I'm really confused now. It took 2.1# and cooled nicely at low speeds (40-50*), but not at highway speed, with no sign of pumping liquid. Now, even at 0.6#, it cools mediocre at idle and still nothing at highway speed. The fun fact is at 0.6#, the top speed is even slower before it stops cooling. 45 with 0.6 vs 60ish with 2.1. Right now I've got 0.6 in it, and have to commute home as I locked my keys in my work truck. Yay.

I need to return the recycler tomorrow morning sometime. Any fresh ideas?

RavenTBK · #12 09-02-2014, 11:07 PM

I now see I'm missing a post in here. After the vacuum I mentioned above, I ended up with 2.1#, vent temp of 42*, pressure at 36/250...which seemed up there on the high side. After reading suggestion of 1.2 and work from there, that then begins my prev reply.

ROLLGUY · #13 09-03-2014, 11:00 AM

On all the systems I have personally installed and have had my local A/C shop vac and charge, I have never put more than 24oz in. The average amount that works best in the systems I have done is 21oz. I have never seen a factory A/C sticker that has more than 2.2 pounds of R12 for the capacity in a W123. The one question I would have is: did you put the PF condenser in upside down?
Although I don't think that is possible with the hoses provided with my kit (#6 hose may not be long enough?), anything is possible......Rich

engatwork · #14 09-03-2014, 12:31 PM

Larger connection at top or bottom on p flow unit installed properly?

RavenTBK · #15 09-03-2014, 02:00 PM

Had to return the recycler.... settled on 1.45# of refrigerant. No clue about what the hell was happening with the 0.x trials. I did notice a slight bit of belt squeal again immediately after charge, but it has been quiet since.

I just went outside and checked the condenser. I dont know which side is supposed to be up, but the shop installed the condenser with the larger connection at the bottom, and smaller at the top, outlets towards the passenger side.

Rich, I also attached a pic of my sticker that shows 2.9# of R12 is specified for my 123.