Automotive Air Conditioning Information Forum

Hi guys, working with a 1997 Gmc 1500 van. The van had rear AC at one time, but has been blocked off with a kit. We had a compressor grenade, so we replaced everything in the system (lines, compressor, evap, condenser, accumulator expansion tube) . Everything is working great at idle. When you start driving it, the high side pressure will rise into the low 400s. Eventually it triggers the high side cutoff and the compressor will shut off. Is this normal operation? Seems fairly high. I have attached pictures as well of the pressure readings. One is at idle and one is after revving the engine for a few seconds. If I shut the system off, the high and low side pressures equalize within 15 seconds. I should also note the system seems to cool quite well even with the high pressure. I feel I should also mention the orifice tube installed is a variable style tube. The system was vacuumed down for an hour and half and the lines were purged of air before charging and the system was charged with 48oz of refrigerant. Thank you.

Link to pictures
https://imgur.com/a/Vymq3uY

How's the fan clutch? All the fan shrouding in place? Did you try misting the condenser or a floor fan in front of the van to see if pressure drops?

Clutch fan is pulling lots of air and the shrouds are all there. Hosing the condenser will drop it down 35-40 psi instantly. Will rise back up quickly

Is the new condenser the same as the old unit?

A 1997 would have had a serpentine condenser about 1.250 thick.

I have seen replacement condensers that are parallel flow units about .75 thick - just like the 2002 & up units. The parallel flow condenser is a good one, but it holds less refrigerant. That is why the 2002 uses a 32 ounce charge for front air only.

If you have the parallel flow unit, recover & re-charge to 32 ounces. The high pressures are typical of an overcharged system.

I never thought of that. The new condenser came with a sticker that said "this unit requires a different charging procedure" but didn't explain what that meant. I'll evac and recharge and let you know.