Not getting desired vent temps after Sanden conversion

[cbjukraine]

I'm running the stock condenser with R12 and saw only about 48 degrees at the vent today on the freeway @60 mph. I stuck my digital thermometer out the window and measured 92 degrees ambient.

I just checked the pressures:

@ idle (with aux fan on)
high side: ~225 psi
low side: fluctuating between 45 and 55 psi

revving to ~2000 RPM
high side: doesn't go higher than 250 psi
low side: doesn't go lower than 30 psi

I've also leak checked the whole system with a halogen sniffer and go no alarms. Any help is greatly appreciated. I want ice cubes blowing out of the vents! This is very confusing, as two summers ago I had a stock working system with R12 and was regularly getting 36 degrees in high 90s Texas heat.

I'm referring to the car in my signature...

[TheDon]

Pretty sure the sanden works better with 134A

[dkveuro]

Originally Posted by TheDon

Pretty sure the sanden works better with 134A

You got anything to back up that statement? Compressor doesn't care what it's pumping. ...only the efficiency of the feon/propane/R12/134a or any other medium has anything to do with vent temperature in any given environment.

If there is leak of coolant heated air into the evaporator housing, or the evap' is partially clogged due to internal corrosion etc etc ...causes temperature changes.

Never found a factory fitted a/c to a 123 that performed flawlessly every season and I have serviced around 200 of 'em.

If you live in a state that allows non SNAP 'freon' you can get vent temp's in 108 degree ambient temp's in the 30's depending on blower/engine speed .

Internal corrosion is often the cause of changing performance from one season to another. Design of condenser helps efficiency as does different 'freons'. Common causes of higher than usual vent temp's is recirculation or blend door not closing.

On a Vanagon, the Sandon SD5 or 7 is about as good as a chocolate tea pot to cool the van in any temp's above 80 F....try 134a in that and see if it helps !

I'm always hearing different theories as to why thing don't work as they think they should from folk who have no experience in anything other than the vehicle they own as the gold standard for all others.


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[TheDon]

OP might need a new ETR or adjust his ETR then.

[dkveuro]

It is possible the TXV is opening at a higher temp reading but that is easily checked. Observing the CC will give you an idea if it's causing the CC to deactivate too early or too often..it's possible the TXV is bad or out of calibration.

A TXV is calibrated differently to R12 as opposed to 134a.


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[cbjukraine]

I'm 99% sure the compressor isn't cycling on the road, so that would lead me to believe the ETR is working properly. What are they set to from the factory, 'cause I've never touched mine?

Originally Posted by TheDon

OP might need a new ETR or adjust his ETR then.

[dkveuro]

Originally Posted by cbjukraine

I'm 99% sure the compressor isn't cycling on the road, so that would lead me to believe the ETR is working properly. What are they set to from the factory, 'cause I've never touched mine?

R12 TXV is usually opening around 36F although i measured a few at 31F (?)
I have not measured a TXV set for 134a as they where all new in the box...all TXV's are now set for 134a.

They are really to stop the evap' core from freezing and from freezing the heater core too. I had a vehicle that actually busted two heater cores in a few months. Turns out the TXV was never turning off the CC and it froze the condensate and then the coolant in the heater core....because the owner...who will remain nameless...said he had antifreeze free at work and would add it later....but never did. I never let a vehicle leave now without antifreeze in the coolant at at least 50% mix. Ho hum...ain't life grand?

BTW...they seem to all close again at 42F.



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[cbjukraine]

Are we talking about the ETR (Evaporator Temp Regulator) or the TXV (Thermal Expansion Valve)?

I was referring to the ETR working because the Evaporator isn't getting cold enough for the ETR to open and cycle the compressor, as I'm not feeling the engine shudder at all on the road from the compressor kicking in.

But my TXV may not be letting enough liquid refrigerant into the evaporator either...

Originally Posted by dkveuro

R12 TXV is usually opening around 36F although i measured a few at 31F (?)
I have not measured a TXV set for 134a as they where all new in the box...all TXV's are now set for 134a.

They are really to stop the evap' core from freezing and from freezing the heater core too. I had a vehicle that actually busted two heater cores in a few months. Turns out the TXV was never turning off the CC and it froze the condensate and then the coolant in the heater core....because the owner...who will remain nameless...said he had antifreeze free at work and would add it later....but never did. I never let a vehicle leave now without antifreeze in the coolant at at least 50% mix. Ho hum...ain't life grand?

BTW...they seem to all close again at 42F.

[TheDon]

Originally Posted by cbjukraine

I'm 99% sure the compressor isn't cycling on the road, so that would lead me to believe the ETR is working properly. What are they set to from the factory, 'cause I've never touched mine?

Jumper the ETR with a fuse or something and retest. Don't do it for too long so you don't freeze the evap.

[dkveuro]

Run following test:

Place vehicle out of the sun. A/C temp' at MAX .... blower speed low. ( Recirc' door closed.) Close all windows and doors. Insert temp' probe in center vents. Run engine at 1800 rpm. After some time temp should drop to 34F to 36F and CC then disengages and vent reading should climb to 38 F or 44 F and CC should engage and vent temp' drop to 34F to 36F again.

If Yes...system working as designed.

If No....Check if system over pressurized and pressure switch cutting CC...( If fitted and operational.)

Check blend doors are fully in Cooling position. Check Recirc' door fully closed.
Check cabin temp' sensor ( Ducted air into center dash small grill.')
Check belt slip at CC.
Check CC slip ( Check voltage and air gap.)

On your figures..Ii would prefer to see lower low side pressures. Minimum 20 psi but lower than 30psi.

Are you using a parallel flow condenser or OE original ?
Does aux fan run whilst CC engaged?

What Sandon are you running? Japanese or Chinese copy?


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[ROLLGUY]

Originally Posted by dkveuro

Does aux fan run whilst CC engaged?


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Try this, you will be amazed at the difference it makes:
MOD- Condenser Fan & Compressor working together by adding a relay

[cbjukraine]

Originally Posted by dkveuro

Run following test:

Place vehicle out of the sun. A/C temp' at MAX .... blower speed low. ( Recirc' door closed.) Close all windows and doors. Insert temp' probe in center vents. Run engine at 1800 rpm. After some time temp should drop to 34F to 36F and CC then disengages and vent reading should climb to 38 F or 44 F and CC should engage and vent temp' drop to 34F to 36F again.

If Yes...system working as designed.

After sitting in the garage overnight, I ran this test yesterday, and the system passed. It's difficult to hold the car at a constant RPM, but it got down to 36*F and the ETR cut the compressor out. I know it did because the engine promptly revved to about 2500 RPM without the compressor load. Temp went up to around 42 and the compressor kicked back on.

I'm still not satisfied, as today, it was in the low 90s and in stop-go city traffic, my vent temps were only in the low 50s. Two summers ago I was getting low-mid 40s in stop-go city traffic. I'm just worried what it's going to be like when the Texas heat hits 100+...

Could I be under or over charged?

Does a 7 cylinder Sanden have less capacity than the R4?

Could my evaporator be oil logged? I know the evaporator is clean, because I had to put a cleaned junkyard one in two years ago to replace a leaky one.

The sight glass is running clear with only occasional whisps of bubbles.

The car sat in storage from 11/2012 to 01/2014, when all the R12 leaked out.

Just trying to give as much info as I can...

[ROLLGUY]

If you are running 134a, the sight glass is useless. You could be over/under charged. I have been running about 20-24 ounces of 134a in my conversions. Even with a PFC, that amount seems to work just fine. If you added much more than a couple ounces of oil to the system, you may have too much oil. The compressor comes with 6 oz of oil, and 8 oz total is about right. If the existing hoses and components have been flushed, then you should be good with the 8 oz total oil. I believe the capacity of the R4 and factory hoses is more than the Sanden and new hoses (a little smaller inside) would be. Running down the road with my 7 cyl in a 300D, 40 deg vent temps were freezing me out of the car (thermometer for monitoring vent temps in center vent). After a while I felt like a side of beef in a meat locker ....Rich

[dkveuro]

As Rollguy says, site glass is not used for checking freon with a 134a system.

If everything is as it was last year and vent temp's are higher then something has changed....disregarding the obvious in that statment, you have to search for something that is not operating, or in the same condition as last year....items I would look for as as follows:

Firewall holes allowing heat in.
Blend door not fully closed.
Fan down stream obstruction.
Fan air entry obstruction.
Door seals still good.
Recirc' door bleeding outside air.
Oil pooling in evaporator.
TXV beginning to fail.
Aux' fans operation.
(ETR passed your test.)
Corrosion internally.
Coolant bleed into heater core.
Suction vane failure in compressor....I would like to see 25 psi low side.
Hose internal failure restricting freon flow.
Condensate drain restricted . Check oe foam drain hose for breaking up.
Humidity changed since last years recorded vent temp's?

Wednesday here in OKC will be 99F at 5pm so I am expecting a rash of calls about a/c performance from several customers.






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[jcyuhn]

Have you made the modification for 100% recirculated air? A standard 123 mixes in 20% outside air even when in recirculate mode. Given the humidity in DFW lately (temp: low 90s, dew point: 72) your discharge temps will be quite adversely impacted by all the moisture which must be condensed out of this air.

I found the a/c in my '84 300D inadequate around town and marginal on the highway in Dallas. Modifying the fresh air door to close when in recirculate mode was good for a ~5 degree drop at the vents on a hot, humid summer day. Somewhere way back in the archives (or on the old Mercedes mailing list run out of Austin - anyone remember that?) is a write up of the process.