AC Orifice Tube

I'll be converting my system to R134a soon enough and over the pat few weeks I've ordered everything I will need but contrary to what I thought I had on hand I'm short a new orifice tube. I understand its a common GM part so I shouldn't have any trouble finding it at my local auto-parts store, but what i'm hoping to learn here is does anyone know the correct part number for this that might be carried at somewhere like oreilys, autozone or even amazon.

Additionally I've read up a little about Variable Orifice Tubes that some some have claimed to have gone with for R134a systems but I cant find much in terms of how well these worked out and if anyone had a part number or source for that as well I'd be curious to give it a go myself.

Im not really wanting to put in an order with a vendor over this small part, I appreciate anyone having any help to offer on this matter.

MT0097-1 for standard or MT0629 for VOV (variable) at Autozone or one that fits an 84 Corvette 5.7 at other stores. I've used both types and with the VOV I would get a weird hissing gurgling noise from the orifice area every time I shut off the AC. I went back to standard and the noise went away. Otherwise, the VOV did work well and I didn't have any other issues with it.

T38623 is what I used! I did have to trim the little nubs off the backside to get a good fit. I think I paid 2.50 for it. Some people have had problems or no benefit with a variable.



Dave B.

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Originally Posted by dn010

MT0097-1 for standard or MT0629 for VOV (variable) at Autozone or one that fits an 84 Corvette 5.7 at other stores. I've used both types and with the VOV I would get a weird hissing gurgling noise from the orifice area every time I shut off the AC. I went back to standard and the noise went away. Otherwise, the VOV did work well and I didn't have any other issues with it.

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Interesting, and thank you for the information. I'm changing my compressor to a Sanden SD7H15 model 4708. I wonder if it will result in a different outcome.

Much appreciate the help gentlemen.

Can't say anything about the Delorean 134A, but on an old Ford truck converted to 134A, I tried both variable and standard orface tubes. Couldn't tell any differnce. Maybe, just maybe, the standard worked better. (Was cooler)

The more it seems I look into the VOV I get the idea that its not the way to go. Higher cost, uncertain benefits/gains, possible noise issues, etc... Perhaps the fixed valve is the winner here. I'll keep it simple.

The problem with the VOV is if your tube has a bend where it sits the VOV will not work.

Supposedly, corvette owners have found that R134a doesn’t get very cold with the standard White Orifice Tube (1.8mm). When I had my car running in 2018, I also found that out. VOV didn’t help me either.

The corvette guys found that downsizing to the 1.6mm Ford orifice tube gives better performance and R-12 like high/low pressures.

So I purchased an orifice tube that is 1.6mm from a 2000 Ford F-250, and I will test how cold it gets once I get my engine back together. Part number 38635.

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Originally Posted by 81dmc

Supposedly, corvette owners have found that R134a doesn’t get very cold with the standard White Orifice Tube (1.8mm). When I had my car running in 2018, I also found that out. VOV didn’t help me either.

The corvette guys found that downsizing to the 1.6mm Ford orifice tube gives better performance and R-12 like high/low pressures.

So I purchased an orifice tube that is 1.6mm from a 2000 Ford F-250, and I will test how cold it gets once I get my engine back together. Part number 38635.

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Something don't sound right to me here??
Using your numbers, you would be decreasing the orifice diameter which would mean the refrigerant would flow through slower. That would mean longer cycle times, which would increase high side pressure. I always heard that people used VOVs on a D to lower the pressure because 134a has higher pressure than R12 (for 70°F and greater, which I know is true). Seems you would be making a bad situation worse. What am I missing?

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Originally Posted by Ron

Something don't sound right to me here??
Using your numbers, you would be decreasing the orifice diameter which would mean the refrigerant would flow through slower. That would mean longer cycle times, which would increase high side pressure. I always heard that people used VOVs on a D to lower the pressure because 134a has higher pressure than R12 (for 70°F and greater, which I know is true). Seems you would be making a bad situation worse. What am I missing?

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I thought the same thing, but with an orifice tube being $3 and easy to replace, I’m up for an experiment.

I’ve never had good ac performance in my car with all new components. I've tried everything but a different sized OT.