AC Compressor Not Engaging - Troubleshooting Help

[MacStainless]

I'm recharging my AC with RedTek today and while doing the recharge, I noticed the AC compressor isn't kicking on. I was able to get about 1 can into the system and had the low pressure holding at about 40PSI. Not wanting to continue charging, I switched into troubleshooting mode which is where I am now and could use some input.

Background
The AC system was empty and held a vacuum for about 45 minutes. I ran my pump for another 45 min on the system in order to evacuate any moisutre. I also put in about 2oz of ester oil. As mentioned above, I was able to get 1lb (1 can) of RedTek into the system but did not proceed further as the compressor wasn't kicking on.

Things I've tried

1. I checked fuse 10 - it's good.
2. I disconnected the wire on the compressor and saw it looked a little cloudy. - I wiped it down and looked okay after some rubbing.
3. With the car off, I tried hand-turning the compressor to ensure it wasn't locked up - I was able to turn it easily.
4. I bypassed the wire on the compressor and jumped it to to the battery post - The compressor clicked on every time I energized it directly.

That's where I'm at. I was reviewing the "how to bullet proof your AC" post (http://www.deloreans.co.uk/forum/showthread.php?tid=5656) on the UK forum and it seems the next step is to jump the low pressure switch. However, on this post (https://dmctalk.org/showthread.php?11695-AC-Low-pressure-adjustment&p=170120&viewfull=1#post170120) Rob Grady says not to futz with it. Also, I'm not sure at what PSI the system should click on. So now I'm not sure how to proceed. I don't think the system will take any more refrigerant without the compressor kicking on. Obviously running it directly jumped is a bad idea, so I can't do that.

Should I sit in the car and try revving up the RPMs? Would that even work?
Should I jump the compressor like the troubleshooting step I tried and leave it energized until the pressure goes below 30 PSI?
Do I attempt to try to add more RedTek into it and hope it kicks on?

If there's suggestions on what I should / could do to get this to kick on and try some simple troubleshooting, it would be appreciated. I don't have a lift or jacks, so under-body work is quite difficult to do.

Thanks.

[David T]

Get a paperclip, bend it open and use it to "jumper" the low pressure switch. Do not let the compressor run much before putting in 2.2 lbs of refrigerant. Best to have the motor running about 1,000 to 1,200 RPM's and have a fan in front of the radiator to help get more air over the condenser. You really should have a set of gauges so you can monitor pressures. This is assuming your vacuum pump can pull a hard vacuum and you got all of the air and moisture out.

[iflights]

Get the AC gauges on the it! You can borrow them from O'Reilly's Auto Parts. No need to invest in them unless you have continuing problems.

[Helirich]

Reving the engine won?t do anything if the clutch isn?t coming in. Jumping the low pressure would be the next step. You?re not going to hurt it for a short run. It?s just to see if that?s the problem. If it works, get a new switch before proceeding.

I don?t understand the guys saying ?get gauges on it?. I assume you have gauges on it. (He said he has 40 psi)

[iflights]

Reving the engine won?t do anything if the clutch isn?t coming in. Jumping the low pressure would be the next step. You?re not going to hurt it for a short run. It?s just to see if that?s the problem. If it works, get a new switch before proceeding.

I don?t understand the guys saying ?get gauges on it?. I assume you have gauges on it. (He said he has 40 psi)

Missed it on the small screen.

[Bitsyncmaster]

You need to warm the can to get your pressure past 40 PSI. As you charge with gas the can gets very cold and therefor drops the pressure. I think you need about 50 PSI to kick the low pressure switch on.

Put the can in a pan of hot water while you charge it.

[MacStainless]

Thanks everyone for the info! I was able to solve this by basically... continuing to charge the system. I resumed the work and began the second can of RedTek. Once the system hit 47PSI the compressor kicked on! I continued to charge it until the can was empty. The compressor kicks off around 24-22PSI. Blows hella cold now, at about 47-degrees at idle.

I did buy gauges and used them the entire time; hitting up Harbor Freight yesterday for all the parts. While I've never had chronic AC issues I did not know if I would have any leaks and figure the tools are an investment. I did look into borrowing the gauges from the local Advance Auto Parts, but I saw a lot of mixed reviews about the kits either leaking or being incomplete.

Anyhow, to make a long story short, I stopped too early and then panicked when the compressor didn't kick on. If I'd just continued charging the system yesterday, I would've been fine.