mcbassin

iTrader: (1)

I know this is an old thread but, I just finished my Vintage air using a stock 4.8 truck a/c compressor. I'm wondering what the pressures should be? It starts off cooling great and my fans come on as they should (using a tertiary switch), then my compressor clutch cycles very frequently. My VA system is pretty old, like 6 years I think. I have working on this project since 2009 and just now getting around to installing it.
There is an temp adjustment **** that doesn't seem to help with the cycling. I'm thinking it's freezing up but not sure what to do next?
Is it under charged? overcharged or just too much compressor for my system.
More about the install HERE
When I first did the evacuation and charge the system worked great and the compressor didn't cycle, I'm wondering if there was some debris or something in my used compressor that could stop up the system? any help?

ls1nova71

iTrader: (4)

It should have cycled from the start, otherwise it will freeze up. Doesnt sound like it is though. If it freezes up, you'll know it because the air will stop coming out the vents. If it doesthat, back off the temp switch just a bit. The truck compressors are not variable so it should work ok. What are your pressures at ?

mcbassin

iTrader: (1)

Hey thanks for the prompt reply Nova. I'm not sure what the pressures are? I can find out this afternoon. You're saying the clutch SHOULD kick on and off? I thought the VA setup just came on and stays on? I appreciate the help brother, I'm lost on this AC stuff.

69 Ghost

How is the system wired? Are you doing this through the PCM. If so it needs to be wired for a fixed compressor and the PCM needs to be setup for it. If you are just running this without the PCM in the loop then it depends on the compressor, etc. I have run the original Sanden, then an R4, and now a Camaro Variable on my setup successfully. If memory serves me right the Sanden ran the lower than the R4. The Variable is a different animal and it runs the low at a higher pressure -215. On a fixed you should be anywhere between 150-190psi on the low side depending on how hot it is.

DW SD

I have a 10S20F denso compressor on my setup with a 10 year old Vintage Air setup - it is working well and cycling. I've seen as low as 37 degree vent temps. My donor is a 2007 Denali (L92 + 6L80).

I chose to do a standalone setup vs. using the PCM to run the compressor. There is a compressor clutch wire (12V+) which calls for compressor from the vintage air controller panel - it is blue. I run that through the high low pressure switch to control the compressor clutch.

When the compressor clutch engages at idle, there is a momentary (less than 1/2 second) of reduced engine speed, then the engine adjusts the upward the idle. It feels a bit like a stumble.

At idle, I see 50 to 55 degree temps depending upon ambient and humidity.

What are your high and low pressures? I'm seeing 25 - ish low and 175 - ish high (from memory) @ the time of charge. Of course, these change with temp and humidity and airflow through the condenser. More or less, my pressures followed a chart like this. http://shbox.com/1/ac_performance_chart.jpg

Doug

mcbassin

iTrader: (1)

The system is NOT wired through the PCM. It is controlled by the switch on the AC control.
I think the truck compressors are fixed stroke, correct me if I'm wrong. My donor is a 2003 4.8 DBW motor.

mcbassin

iTrader: (1)

Thanks Doug, It sounds to me like you have the same setup I have on my truck. Yes at idle the clutch cycles on and off repeatedly. Not sure what it will do when driving? as I haven't got mine ready to drive just yet. I am wanting to make sure if I need to change the compressor or setup any way, I can do it while the front sheet metal is still off.
It's easy to work on right now with no fenders or hood. less chance of scratching my new paint too.
I will hook my gauges up tonight so I will have some data to compare.
Thanks again.

mcbassin

iTrader: (1)

It looks to me like my high side pressure is too high. The high side pressure was around 280 from the start.
I forgot my temp probe at work so I couldn't measure the air temp in the cabin but it feels cold.

This quick video of the gauges when it started cycling. Air temp was 87 humidity was 20%. I am using R134 gas. The loud noise you hear is the dual fans running not the engine racing.

VIDEO

Any ideas of what could be causing this kind of symptom? I'm wondering if it's over charged?

DW SD

Hi,
I watched the video and compared pressures to a few charts. I think you are overcharged by a little bit.
I think the high pressure switch should dis-engage about 400 psi. That could add to your cycling issue. If the pressure gauge is slightly inaccurate or the switch a little less for its threshold, this could be the issue.

Aim for 25 psi on the low pressure side at that temp (89 w/ low humidity). Or refer to the chart link I posted and aim for the lower pressure on the low side given the range and ambient humidity and temp.

Doug

DW SD

also, lack of airflow through the condenser will contribute to high high side pressures. Does your cooling fan draw air through the condenser effectively? If not, use a household fan to add cooling and see what happens.

mcbassin

iTrader: (1)

Thanks Doug. I called Vintage Air this morning, their tech support guy told me to shoot for no more than 250 on the high side. He said the head pressure is too high. He also said it is definitely over charged. I installed approx. 2.5 12 oz. cans of R134 when I charged it. He said he always recommend starting with just 2 cans. My first goal is to get that high side pressure down.

On the fans, in my opinion they are getting plenty of flow across the condenser with both running on high speed setting. I say this because from the time I start the system to the time it starts cycling frequently is less than a minute.

DW SD

You could always put a household fan in front and see if the pressure changes. If so, then you'd know you could be getting more airflow.

I wonder if Vintage Air tech support is a seasonal job They must be slammed early each Summer.

Doug

DW SD

Let us know what happens when you remove some of the refrigerant. A shop will likely take a bit out for free. Not supposed to bleed to the atmosphere.

I wondered if one could evacuate a propane tank and then remove refrigerant from the high side to pressurize the tank and keep it for later use.

mcbassin

iTrader: (1)

Not sure about the propane tank idea but I'm pretty sure my HVAC buddy has a recycling system. He owes me a favor

DW SD

I checked pressures / temps on my system. Thought it might help. Definitely are lower than what you have measured.

I'm seeing vent temps 37F to 40 and Condenser temps of 125F ish.

Doug

DW SD

Here's a few shots showing temps I'm measuring.
One more thing. Here are the charging instructions: http://www.vintageair.com/Instructions2013/900004.pdf
Doug

mcbassin

iTrader: (1)

Thanks Doug. Great looking truck too.

My finding was the system was over charged. I was able to dump some of the gas and the pressure went down to the 250 range and it's not constantly cycling the clutch on the compressor now. Air is pretty cold, not sure the temp, I forgot my gauge at work again. Thanks for all the help guys.

DW SD

Great!
I bet the high pressure switch was interrupting the 12V+ to the compressor clutch, causing yours to cycle quickly. I noticed yesterday at idle, my compressor stayed on for a while was I was taking pictures.

Also, when you hook up the gauges take a close look that the needles don't flutter. Apparently, that is a sign of a bad reed valve in the compressor.

I also learned recently not to turn the refrigerant bottle upside down or to shake it. That can add too much refrigerant in one shot to put the compressor to where it attempts to compress liquid (which breaks the reed valve).

Thankfully, I didn't do that.

Doug

Phillipm

iTrader: (2)

This is an old thread, but I was looking for something else and ran across this I felt like adding my experiences.

For anyone in the future, I fought my Vintage Air Gen IV unit quickly cycling going down the road but it worked perfectly at idle. After 2 years, 2 different Gen IV evaporators, multiple diagnosis with VA techs. We learned that the Denso 10S20F and 10S17F compressors (sized for larger late model orifice tube systems) are just too big of a pump for the smaller evaporator core in the VA system. I finally switched that to a Sanded SD5H14 (508), it worked well going down the road but was just passable at an idle in my K5 blazer here in the Phoenix summer. I switched to the Sanden SD7H15 or the (709) as VA refers to it as, and have found a happy medium. It still doesn't cool as well as my 10S17F did at an idle but it is much more stable at controlling the evaporator temperatures 1500-2000 rpm once the truck cools down. So, if you've experienced something like this, I would suggest looking at going to a smaller compressor from the Denso GM truck line.

dannyual777

Phillip, thank you for coming into this thread and posting your detailed information. Your detailed write up could really help someone who is having similar problems. I don't have a Vintage Air system but I do my own automotive ac work and years ago I converted my 1991 Mustang GT from R12 to R134a. I've got all of the automotive ac tools including a vacuum pump.

My new project is my 4cyl '91 Fox Body Mustang coupe. I'll be putting those ac tools to use with this car much later on. My LS480 and T56 Magnum are still in their crates so it's going to be a while. Anyway, I'm always interested in automotive ac threads. I live in north Houston, TX after all!!!