I want to test the pressure in the aircon system to see if the garage has put too much refrigerant in the system. The noises only started after the recharge.
Can anyone recommend a cheap, half tidy, refrigeration aircon manifold gauge Set?
Does anyone know the data for the high and low side pressure, that is correct for the Omega aircon system and @ what idle speed please?
Grrrr. Power cut after typing in a long reply. Effing national grid. Anyway...
It's actually illegal to work on a charged A/C system without the right qualifications. Which basically means you need an expensive but worthless training course, and a piece of paper with a tick in the right box from the nanny state. So with that in mind...
You can buy AC gauge sets off eBay easily enough, and they'll work. The problems are normally with getting the couplings onto cars filler ports to seal properly. Cheaper couplings tend to leak. However, even if you get the gauges to seal properly they won't tell you much more than you already know. A/C systems aren't filled by pressure, they're filled by mass(weight). The pressures vary by as much as 2:1 depending on the ambient temperature. The filling machine has a set of scales in it, and it measures the weight of the gas cylinder before and during filling. Once the correct mass of gas has been filled, the machine stops. I can't remember the correct weight for an Omega - something like 1.1Kg?
With the engine not running, the low and high side ports will both show the same pressure - probably somewhere between 40psi(cold day low gas filling) and 100psi (very hot day, very full gas levels).
With the engine running, the high side will increase rapidly to between about 150psi and 300psi. The low side will drop slightly to probably somewhere between 30psi and 50psi.
The compressor is protected by both low and high pressure cut-out switches. If the pressure is too high or too low the compressor will either never turn on, or turn on and off again. It's quite difficult to damage anything by overfilling. Much more likely to damage it by not putting any oil in, or using the wrong sort of oil.
In short, if the top pipe is getting cold, and the compressor is staying engaged all the time (the triangular plate on the front of the compressor spinning) then there is likely to be acceptable levels of gas in it. If you suspect something is wrong, I'd take the car to a different A/C garage and ask them to test it. There may be a nominal charge (£10-£20) but as long as they don't have to drain it all down and re-charge it then you shouldn't have to pay for a full re-charge.