Automotive Air Conditioning Information Forum

Here is the issue I am having: High high side pressures (up to 375psi @ 2K rpm) with low side around 20-24psi. Vent temp 39F with outside temp 70F.

Here is what I have done: This is an aftermarket in-dash Behr AC unit in an 83.5 VW Vanagon, which I have replace everything except for the electronics and the evaporator, everything else was replaced with new (Compressor: Sanden SD7H15, parallel flow condenser from GoWesty, drier w/ binary switch, expansion H valve, and hoses). I flushed the evaporator, blew it dry, and let it sit for a couple of days before reassembly. The vent motors were oiled and tested fine, the controls were checked and failed potentiostat replaced, and wiring for rad fan and binary switch was corrected.

Since system was all new and clean I added approximately 2.2oz of extra Sanden SP-15 oil; 0.5oz (15cc) for condenser, 1.5oz (44cc) for evaporator, .2oz (6cc) for the hoses. I could only get about 1oz of oil in the hose just before the expansion valve going into the evaporator so the other .5oz went into the condenser. The system was then pumped down using a high vacuum pump from a SEM for about 30 min. Vacuum held the Harbor Freight gauge pegged at max vac for a week.

Charged system with ~4 cans of eco friendly refrigerant. Connected first can, purged line and charged liquid into high side. Closed high side valve on gage and replaced can of refrigerant but did not purge line. Started van with AC on max and a box fan in front of condenser. Opened low side vale and slowly emptied can using heat from exhaust, keeping upright to only dispense gas. Did the same for the third can. The low side pressure was rising but still below 20psi, the high side was about 250psi. 4th can I stopped about half way because the low side was not changing much but high side was climbing, especially when I would increase rpm. This is when I fix some wiring and the radiator fan now comes on when compressor engages. This helped drop the pressure on the high side (~250psi) but the low side was still below 20psi so I added the rest of the 4th can. Now the low side is between 20-24psi but the high side is still too high.

With the ambient temp about 70F, the van idling @1100rpm, when the AC is first turned on and the compressor initially engages, the low side drops quickly to about 30psi and the high side will be around 150psi. The high side then slowly climbs to about 225psi and stabilizes while the low side slowly drops to about 19psi (vent temp ~41F). The next cycle of the compressor will have the high side stabilize around 250psi and the next cycle 275psi, then next cycle 300psi. It will then stay between 275 and 300psi, all the while the low side is at ~19psi and the vent temp drops to 39F. If I rev the engine to 2000rpm, the high side can go up to 375psi or more while low side is around 20-24psi.

Using an IR gun, temp at condenser in, is about 105F and at outlet it is 65F. I could not find anything that seem to indicate a blockage. I do need to remove the grill and get some better temp readings with a surface thermocouple.

What does the internet wisdom have for me? From what I have read, I am leaning towards an expansion valve that is defective or not tuned properly for refrigerant. Any other ideas? Too much oil or too much oil in the wrong place? Over charged with refrigerant?

Vanagon aftermarket AC used Diesel Kiki with more oil than Sanden. Need to remove that oil or decrease oil in Sanden crankcase.
Too much oil decreases heat transfer inside heat exchangers and lowers refrigerant mass flow.
Sanden compressor is sold with enough oil in the crankcase for your application without adding any harmful oil overcharge.
Consider a pusher fan on the front of the condenser for higher ambient.
If TXV is contributing to high discharge pressure then suction line will frost and suction pressure will increase.
hotrodac

Why did you not purge for the second can. Always a pleasure to get hard info from Ice!

Ice-In-Tropics: Since everything was replaced, there was no oil at all in the system to begin with. I know that the new Sanden compressor came pre filled but I was under the impression that some oil still needs to be added for the other components that will end up being coated with the oil. With the Vanagon engine being in the rear of the vehicle, there is ~14ft each of #8 and #10 size hoses running to and from the front condenser & evaporator. Are you saying the the charge of oil in the new Sanden compressor should have been enough for the whole new system?

Is there a way of removing the excess oil without opening up the system and having to recharge?

tbirdtbird wrote: Tue Jun 04, 2024 1:29 pm Why did you not purge for the second can.

I am a newbie and thought the yellow hose sealed when I removed the previous can of refrigerant so purging would not be needed. After I finished charging the system I realized the error in my assumption.

In that case you have introduced atmospheric air which we term a non-condensable. This will cause an unnecessary increase in the hi side.
If it were my system, I would change the drier , evacuate, vac, and recharge to spec. Charging into the hi side with engine off is actually a good approach since the comp will have plenty of refrigerant at startup. Charging with cans is awkward compared to a canister. You need to be sure to purge lines whenever a can is connected or changed.
Carefully study where the shraders are in the hoses and you will be better off

I will let Ice continue about your oil. You may not realize it but he is a premier consultant, and wrote the book ‘Hot rod AC’, a book worth getting

tbirdtbird wrote: Tue Jun 04, 2024 2:14 pm I will let Ice continue about your oil. You may not realize it but he is a premier consultant, and wrote the book ‘Hot rod AC’, a book worth getting

Thank you for your help so far and the info on Ice. I am thrilled to know that I am getting advice from an expert and not just some Joe Shmoe on the internet.

Ummmm no Joe schmoes here. Tim has assembled the best group of advisors I have ever seen. Ice was involved in developing what we now know as a Sanden.
His book is ‘How to air condition your hot rod’.
I stand corrected on the title I gave before.

Some of the advisors here have advised the military, to name just one more feather in the cap

"Eco Friendly Refrigerant" What would that be exactly?

The replacement blends of R600/R290 should be charged differently to begin with. Charge as a liquid. The blends are less dense than R12, and overcharging is easy to do.

Blends can run lower pressures on the low side. 18-25 psi on the low side would not be a surprise. Trying to hit a pressure by adding refrigerant can lead to overcharge too.

I find your numbers a little confusing. An ambient temperature of 75F, Condenser is 105F in and 65F out. Are you spraying water on the condenser to get it below ambient?

And yet the high side is hitting 375psi @ less than 150f?

Is the dryer installed in the proper flow direction? Any cold spots on the low side line?