Auto Air Conditioning & Heater Repair: 2003 Tahoe AC High Press, chev tahoe, floor fan

Question
Hi John,
I had a my 2003 chev tahoe intermittantly blowing less than cold air. Shop vacc'd it down checked for leaks and recharged. They are telling me that the HIGH side press g0oes way up +400Psi so they stopped. They replaced oriface tube incase of blockage & now wondered if the condensor was getting enough heat exchange?? They place an additional floor fan infront of the grille and the pressures dropped?? How do I t/shoot this??
1. I will wash ot the condensor to ensure there is not blockages externally with fins.
2.I have heard the thermo condense fan operated by a press switch earthed thru the eng ECM??
They have left the system vacc'd out untill we can get it back to them. Is there any checks I can do in the interim. They checked my visc fan drive and it seems ok!!
Can you assist??
Anth

Answer
Hey Anthony,

  If the shop put a fan in front of the condenser and the pressure dropped that’s your answer right there, because heat causes pressure so less heat, less pressure. Now you can clean out the condenser and see if that makes a difference but I think you’ll have better luck replacing the condenser, because there could be a blockage within the condenser causing the pressure to go way up. You could add the fan as well but make sure you don’t half ass the wiring on the installation so you don’t kill your ecm.  As far as checking for now you can’t really do anything to check with no refrigerant in the system.