Help with variable displacement dual evap system!

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Seraslibre
Posts: 3
Joined: Wed Sep 14, 2016 8:02 pm

Help with variable displacement dual evap system!

Postby Seraslibre » Wed Sep 14, 2016 8:19 pm

I'm fairly experienced doing ac work, but I'm stuck in a rut.

Vehicle in question is a 2007 Toyota Sienna. It uses a variable displacement compressor with a magnetic clutch. There are two evaporators - one up front and another in the rear of the van. System Freon capacity is 27.5oz of R134a.

To understand where I am now I will first detail the sequence of events that led me to this point;
1. AC had been getting weaker over the summer, but worked. I decided to evacuate system and replace two o-rings on the refrigerant lines that run to the evaporator in the rear cooling unit. This is a known a weak spot on these vans and typically where Freon leaks start. After I replaced the O-rings I pull a vacuum on the system and try to charge it. However, I can't get more than 5 ounces of refrigerant into the system. In addition, the high and low side pressures are identical @ 100psi. To me this is either a compressor failure or a variable displacement valve failure. I purchase a new compressor that comes with a new variable displacement valve and installed it today.
2. After installing the new compressor I pull a vacuum on the system and proceed to charge the Freon. As is typical I begin charging the high side with the vehicle off until I cannot get any additional Freon into the system. I jump the magnetic clutch on the compressor and then start the car. Next I slowly allow for freon to enter the low side. I end up with 65psi in the low side and 50 on the high side. I can only charge ~7 oz of Freon.

What am I doing wrong here?
GM Tech
Posts: 145
Joined: Fri Apr 22, 2016 7:22 am

Re: Help with variable displacement dual evap system!

Postby GM Tech » Thu Sep 15, 2016 5:31 am

5 ounces-- really? I assume you are using a machine instead of cans-- I would say from here that your machine is almost empty---there should be no problem putting the entire charge in the system in the high side after vacuum- Only time I have your issue is when my tank on my machine is near empty. Never never ever judge a variable (or any other) compressor that is on a system WITHOUT the proper refrigerant charge in it. Get the right charge in it and then test....your machine is either low, or your gage connectors at the car are amiss- pulling vacuum on only the gage set- and not the system- 5 ounces sounds like you charged the hoses only and read the pressures of the hoses only- just as if the hoses were never connected to the car....there is also the possibilty that your tank is full of air- attache a gage set directly to your tank- at 80 degf- it should be near 85 psi---if over 100 psi- you have recovered a bunch of air-

When you pulled a vacuum- did it act normal? did it take a minute or two to pull down?, or did it pull down in 10 seconds?--that is a big hint-- the volume of air would tell you if you pulled on the gage set hoses only.
Seraslibre
Posts: 3
Joined: Wed Sep 14, 2016 8:02 pm

Re: Help with variable displacement dual evap system!

Postby Seraslibre » Thu Sep 15, 2016 7:02 am

I'm starting off with a new Freon tank, so that is not the issue.

I'll look into the gauges/fittings being the issue and will report back what I find.

When pulling a vacuum it took ~5 minutes to get to 29mmhg. Is it possible the manifold set or the schrader valves work on vacuum but obstruct inflow? When I evacuated the system it worked fine using all the same hardware (manifold set), so I'm perplexed as to what would change that would prevent me from filling the system.
Seraslibre
Posts: 3
Joined: Wed Sep 14, 2016 8:02 pm

Re: Help with variable displacement dual evap system!

Postby Seraslibre » Thu Sep 15, 2016 7:41 pm

Problem remains.
Did this tonight;
1. Removed valve cores and checked for leaks - all ok.
2. Verified in and outflow through each valve core (hi/lo sides) both with and without manifold set - all ok.
3. Blew compressed air through high and low sides - and verified I have flow in the circuit - Air comes in through one side and out through the other and vice versa.
4. Evacuated system - took about 7 minutes to get to 29mmHg. Continued pulling vacuum for about 20 minutes.
5. Charged high side with liquid - took 17.5oz and got to 70psi on high and low sides. Closed manifold valves.
6. Started van. Low side went to 77psi, high side stayed at 70psi. Accelerated to 3krpm - still no change. Didn't bother trying to charge gas into the low side as the pressures were high enough that nothing would change.

I'm starting to suspect the variable displacement control valve for the compressor is not getting a signal to maximize compressor displacement. How do I check for this? When I unplug the control valve nothing changes on the compressor.

At a loss here - any other ideas? Again - system was working fine until I evacuated it to fix a leak, so I'm struggling with what could have gone wrong after discharging the system to repair the leak.
GM Tech
Posts: 145
Joined: Fri Apr 22, 2016 7:22 am

Re: Help with variable displacement dual evap system!

Postby GM Tech » Fri Sep 16, 2016 5:13 am

If control valve has a wire to it- then it is a pulse width modulated control valve. meaning the a/c controller "shoots" 12v at it to adjust it- much like a servo motor- so in some cases , there is no magnetic clutch (2012 chevy cruze for example) and the a/c relay is in the circuit to the control valve, along with an a/c fuse, I believe. Does yours have a clutch- with a coil wire? or just does the wire to the compressor feed only the electronic control valve? If so, you need to check the circuitry and wiring back to the a/c relay.......hope this helps.
mk378
Posts: 78
Joined: Tue May 24, 2016 5:53 am

Re: Help with variable displacement dual evap system!

Postby mk378 » Fri Sep 16, 2016 8:14 am

Whenever someone reports they see the high side a lower pressure than the low side, that almost always means that the couplers on their manifold aren't engaging the ports on the car properly.
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wptski
Posts: 82
Joined: Thu May 12, 2016 5:53 am

Re: Help with variable displacement dual evap system!

Postby wptski » Fri Sep 16, 2016 9:10 am

mk378 wrote:Whenever someone reports they see the high side a lower pressure than the low side, that almost always means that the couplers on their manifold aren't engaging the ports on the car properly.

That's only 7psi difference and all analog gauges are more accurate in the middle third of their scale.
tim73
Posts: 1
Joined: Sat Oct 07, 2017 9:27 pm

Re: Help with variable displacement dual evap system!

Postby tim73 » Sat Oct 07, 2017 9:44 pm

Did you ever find the fix? I am facing something similar.

2009 Sienna, with intermittent working AC. So far, new compressor, condenser, front expansion valve, and all rear lines were replaced. I was able to pull down 29" for about an hour, then it sat for an hour, and didn't loose any vacuum. So, it seems tight. I filled it up with refrigerant, I put in 2 and half cans. So, now when I run the AC, I get 225 high side and 55ish on the low side. about 68F at the vents, with about 85F ambient. It will do this for about 10 minutes or so(At idle) but then the high side falls to 150or so and the low side jumps to 85-90. When it was at 225 & 55 the high side pipe was cold, low side was warm. When the pressures change, the high side goes warm, and the low side gets so hot I can barely touch it. The condenser fan is coming on and off..its variable...so I assume its doing what it should do.

When I replaced the condenser, the desiccant sock was pretty nasty with black crap, so I have cleaned out the lines best I can. I am not familiar with the variable compressors...ac amplifiers etc. Tomorrow, I plan on replacing the rear expansion valve. Ideas? Thanks!

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