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turbo ac issues

TimS

Member
Joined
Dec 18, 2017
So I've done a bit of work on my Kjet turbo ac system. It blows cold (low 40s) at idle and around town, but on the freeway it starts getting warm at around 2500rpm and up. I've tried to keep out of boost best I can to see if it makes any difference. When I get off and keep the rpms low it slowly starts blowing cold again.

I have replaced the heater valve and the interior vents are mostly holding vacuum. The compressor seems to be on when I'm on the freeway, I've cycled the ac switch off and on and can see the voltage drop.

New lines. new p-flow condenser, sanden clone, flushed the original expansion valve and evaporator. Adjusted the expansion valve with the allen. 35/240 psi while at idle.
134a

I know that the compressor should cut off when the car goes into full boost. I've checked the wiring diagrams but it is a little vague. I would think that at full throttle it turns off.
Any ideas?
 
I can check if its backwards, but pretty sure.
I thought if its overcharged the low pressure side would be higher. If its overfilled would it get would it get cold at all? With the new condenser not sure what would be a proper fill amount.
The sticker says 2.9lbs. So I guessed at about 80% of that.

And thanks for any suggestions. Willing to try it all.
 
Saw your pressures which seem ok but at what temp was it outside? Also most expansion valve I’ve bought for 134a were 7 turns out. Did you use vacuum pump to pump system down?
 
I still think 250 PSI (high side) is too high. I like to see the high side only at about 150 PSI.

I was thinking that maybe your high side is going up TOO high and cutting out the compressor at higher speeds/RPMS.
 
I still think 250 PSI (high side) is too high. I like to see the high side only at about 150 PSI.

I was thinking that maybe your high side is going up TOO high and cutting out the compressor at higher speeds/RPMS.

At what temperature?
Pressure readings mean nothing without ambient temp.
OP, also need to be checking at 2k rpm fast idle.
The following is a cheat chart, but if your pressures aren't close ish you may have other issues.
 

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There is no high pressure cutoff switch on a 240 AC system. IIRC the older systems had no pressure switches at all. Later systems have a low pressure cutoff and a high pressure switch that turns on the fan, but doesn't kill the compressor.

OP - your symptoms (low side normal / high side high) might be caused by air in the system, according to a very nice AC troubleshooting chart made by Sanden. If you can get to a shop that has AC recovery equipment you can have it fully evacuated and then recharged.

I would also check the condition of the evaporator (inside the dash) - there is no cabin air filter in a 240, and the evaporators get clogged up with dust, leaves, and other debris. Also check your blend doors and heater valve - there could be a situation where the AC is working fine, but a blend door issue is letting hot air or ambient air come in to the ductwork and cancel out the cooling effect.
 
There is no high pressure cutoff switch on a 240 AC system. IIRC the older systems had no pressure switches at all. Later systems have a low pressure cutoff and a high pressure switch that turns on the fan, but doesn't kill the compressor.

OP - your symptoms (low side normal / high side high) might be caused by air in the system, according to a very nice AC troubleshooting chart made by Sanden. If you can get to a shop that has AC recovery equipment you can have it fully evacuated and then recharged.

I would also check the condition of the evaporator (inside the dash) - there is no cabin air filter in a 240, and the evaporators get clogged up with dust, leaves, and other debris. Also check your blend doors and heater valve - there could be a situation where the AC is working fine, but a blend door issue is letting hot air or ambient air come in to the ductwork and cancel out the cooling effect.
http://www.sanden.com/objects/3_-_Troubleshooting_-_Web_01.pdf
 
Also OP, you can use this chart and static charge pressure and temperature to determine if you have air in the system:
 

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As a general rule, i expect to see the high side at about DOUBLE AMBIENT temp. (Degrees F multiplied by 2= approx high side)

Your second pic (Volvo manual) shows high side readings should be under 200 psi.

I work on modern cars, and not old modified/retrofitted systems, so things could be a little bit different. I just know that on the modern cars that I work on, once the high side starts getting above 200 psi, the electric fans start kicking on stronger and the compressor may disengage a little past 200 psi.
 
Your second pic (Volvo manual) shows high side readings should be under 200 psi.

That's only valid for ambient temps of 86 degF and below. At 104F ambient the high side pressure Volvo is saying it can be well over 200 psi as shown in the two tables. TimS needs to specify what ambient temp was when the pressure readings were taken. It stands to reason that somewhere in the 90s it would cross the threshold into 200 psi being acceptable.

Also, TimS, at anything above idle the low side pressure will start to drop and high side will rise, so keep that in mind.
 
That's only valid for ambient temps of 86 degF and below. At 104F ambient the high side pressure Volvo is saying it can be well over 200 psi as shown in the two tables. TimS needs to specify what ambient temp was when the pressure readings were taken. It stands to reason that somewhere in the 90s it would cross the threshold into 200 psi being acceptable.

Also, TimS, at anything above idle the low side pressure will start to drop and high side will rise, so keep that in mind.

The Verdant Volume suggests this should be tested at 2k rpm not idle.
 
Another thing to check is heat shielding between the turbo and high side AC lines going into the evaporator. On the highway at higher engine speeds you may be heat soaking the refrigerant before it makes its way into the condenser. Granted, you will have more airflow through the engine bay at highway speeds, but also more heat coming out of the engine & turbo for longer sustained periods.
 
The Verdant Volume suggests this should be tested at 2k rpm not idle.

Yeah that's what I was referring to. The pressures will change as engine idle speed changes so it's important to note at which speed the limits are specified.
 
A lot here
So I did vacuum out the system system.
The temps were in the high 80s with those pressures which seem to match up with the chart. Although looking it seems like the low side is lower. I read that when the system is overfilled the low side starts to bet higher and then it cant ‘ expand’ and cool.
It is 134 which from what I’ve read runs at higher pressures.

I did spend a lot of time fooling around with climate control stuff blend doors and heater valve. It all seems to be working.
Because it is cold at lower speeds, I don’t think the evaporator is covered but can’t say for sure. Is there a way to clean it with out discharging ?
I will check the ambient temp/ pressure. It is possible that I’ve contaminated by not bleeding the gauge lines with 134 before flowing it into the system.
I keep going back to the boost switch cutting out the compressor.
 
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